I can’t wait to share my Gruyere Mushroom Caramelized Onion Bites, where smoked applewood gruyere, mushrooms and caramelized onions tuck into flaky puff pastry for a quick, make-ahead appetizer that hides a little twist.

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I’m always on the hunt for party snacks that look fussy but dont take forever. These Gruyere Mushroom Caramelized Onion Bites do that trick: flaky puff pastry layered with smoked applewood gruyere for a little smoke and rich texture.

Theyre quick, easy to assemble, and perfect to make ahead so you can actually enjoy the party. Think Mushroom Puff Pastry Pinwheels energy but more grown up, bite sized and sturdy.

They disappear fast, I swear. Ive learned a couple real life hacks to speed prep and keep them crisp when reheating, cause I mess up timing all the time.

Ingredients

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Flaky, buttery layers, high in carbs and fat; makes bites rich and crisp.
Sweet when caramelized, it’s full of fiber and cancer-fighting quercetin.
Earthy, umami boost, low calorie, adds meaty texture and B vitamins.
Butter gives richness and browning, olive oil adds healthier fats and flavor.
Melty, smoky, sharp cheese; adds protein, depth and a salty kick.
Optional tang, low calorie, cuts richness and gives a little zip.
Thyme gives herbaceous lift, pepper adds warm bite, both low calorie.
Gives glossy, golden finish and helps toppings stick, adds tiny protein boost.

Ingredient Quantities

2 sheets frozen puff pastry, thawed (about 17 x 11 inches each)

3 medium yellow onions, thinly sliced, about 4 cups

2 tablespoons unsalted butter

1 tablespoon olive oil

1 teaspoon granulated sugar

1/2 teaspoon kosher salt, plus more for seasoning

8 ounces cremini or baby bella mushrooms, sliced

1 tablespoon unsalted butter for mushrooms

6 ounces smoked applewood gruyere, grated

1 large egg, beaten (for egg wash)

1 tablespoon Dijon mustard (optional but good)

1 teaspoon fresh thyme leaves, chopped, or 1/2 teaspoon dried thyme

Freshly ground black pepper, to taste

How to Make this

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1. Preheat oven to 400°F (200°C) and line a baking sheet with parchment, keep a rack in the middle of the oven. Make sure the puff pastry is thawed and still cold before you roll it out.

2. Heat 2 tablespoons unsalted butter and 1 tablespoon olive oil in a large skillet over medium low heat. Add the thinly sliced onions, 1 teaspoon granulated sugar and 1/2 teaspoon kosher salt and cook low and slow, stirring every few minutes, until deeply browned and sweet, about 25 to 35 minutes. If they start to stick, add one to two tablespoons water to deglaze the pan. Set onions aside.

3. In a separate skillet melt 1 tablespoon unsalted butter over medium high heat. Add the sliced mushrooms in a single layer, salt lightly and let them brown without crowding. Stir occasionally until the mushroom liquid has evaporated and they are golden, about 6 to 8 minutes. Stir in the thyme and some freshly ground black pepper, then remove from heat.

4. Grate the 6 ounces smoked applewood gruyere while cold, it shreds better that way and melts nicely later.

5. Lightly flour your work surface if needed and roll each puff pastry sheet gently to even it out, keep it cold. If you like a little zip spread about 1 tablespoon Dijon mustard across each sheet, this is optional but good.

6. Cut each pastry sheet into roughly 2 inch squares (you can do bigger if you want fewer bites). Place squares on the prepared baking sheet about an inch apart. Spoon a small mound of caramelized onions onto each square, top with a few mushrooms, and sprinkle grated gruyere evenly so each bite gets cheese.

7. Either fold opposing corners up to make little parcels or just leave them as open tarts, either way press edges lightly to seal if folded. Brush each pastry generously with the beaten egg for a shiny golden finish.

8. Bake on the middle rack until the pastry is puffed and deep golden, about 12 to 16 minutes. Watch closely near the end because ovens vary.

9. Let cool a few minutes on a wire rack, then finish with a few extra thyme leaves and more freshly ground black pepper to taste. Serve warm.

10. Make ahead tip: you can assemble these and refrigerate up to 24 hours or freeze tray first then transfer to a bag. Bake from refrigerated add a few minutes, bake from frozen add about 4 to 6 minutes and check for doneness.

Equipment Needed

1. Rimmed baking sheet lined with parchment paper
2. Large skillet for the onions
3. Medium skillet for the mushrooms
4. Rolling pin (keep the pastry cold)
5. Sharp chef’s knife and cutting board — you’ll use both a lot
6. Box grater for the smoked gruyere
7. Wooden spoon or silicone spatula for stirring
8. Small bowl and pastry brush for the egg wash
9. Wire cooling rack and oven mitts for handling hot trays

FAQ

Q: How long should I cook the onions so theyre properly caramelized? A: Plan on about 25 to 35 minutes over low to medium low heat. Stir every few minutes, scrape the brown bits off the pan, and add the teaspoon of sugar and half teaspoon salt early to help them sweeten and brown. If theyre browning too fast lower the heat, patience is key.

Q: Can I make parts of this ahead of time? A: Yes. You can caramelize the onions and sauté the mushrooms a day or two ahead, cool them and store in the fridge. Assemble and bake the bites the day you want to serve. Or assemble unbaked bites on a tray, freeze until firm, then transfer to a bag and bake from frozen adding about 5 to 10 minutes to the bake time.

Q: How do I keep the puff pastry from getting soggy? A: Work with cold pastry and preheat your oven well. Don’t overload the filling, drain mushrooms well and cook off their liquid, and brush the pastry with a thin layer of egg wash or a little Dijon where the filling will go this creates a small barrier so the pastry stays crisp.

Q: My mushrooms released a lot of water, any tips? A: Cook them in a hot pan with the tablespoon of butter, give them room so they brown, and don’t salt them until most of the water has evaporated. Salt early draws out moisture so wait until the end for better browning.

Q: What can I use instead of smoked applewood gruyere? A: Good swaps are smoked gouda, regular gruyere, fontina, or a sharp white cheddar. If you want less smoke choose a milder cheese, or mix cheeses for more depth.

Q: How do I store and reheat leftovers? A: Keep leftovers in an airtight container in the fridge for up to three days. Reheat in a 350 F oven for about 8 to 10 minutes so the pastry crisps again, or use a toaster oven. Microwave will make them soft so avoid it if you want crispness.

Caramelized Onion Puff Pastry Bites Recipe Substitutions and Variations

Puff pastry: phyllo sheets (brush melted butter between layers for crisp), store bought pie crust (denser but works), crescent roll dough (rises softer, more buttery)
Yellow onions: Vidalia or other sweet onions (even sweeter so cut added sugar), shallots (milder, more delicate), red onion (adds color and a bit of bite)
Smoked applewood gruyere: aged white cheddar (sharp, melts well), smoked gouda (keeps smoky note), Emmental or regular Gruyere (less smoke, classic melt)
Cremini mushrooms: white button mushrooms (milder but same texture), shiitake (meatier, deeper umami), portobello (slice thick, big mushroom flavor)

Pro Tips

1. Keep the puff pastry stone cold right up until baking, dont overwork or roll it too thin or it will get greasy and wont puff, and if it softens just stick the tray in the fridge for 15 minutes before baking.

2. Caramelize the onions low and slow and be patient, stir only sometimes and if they start sticking splash a bit of water or a little vinegar to deglaze, that acid will lift the brown bits and make them taste way better.

3. For mushrooms use a wide pan and cook in a single layer on fairly high heat, salt toward the end not the start so they brown instead of steaming, and if they still give off too much liquid blot them with paper towel before assembling.

4. Grate the gruyere cold for cleaner shreds, brush edges generously with egg wash for color, and if you want to prep ahead freeze the assembled pastries on the sheet first then bag them; bake from frozen and add about 4 to 6 minutes but watch the oven near the end.

Caramelized Onion Puff Pastry Bites Recipe

Recipe by Tina Bueller

0.0 from 0 votes

I can't wait to share my Gruyere Mushroom Caramelized Onion Bites, where smoked applewood gruyere, mushrooms and caramelized onions tuck into flaky puff pastry for a quick, make-ahead appetizer that hides a little twist.

Servings

servings

Calories

490

kcal

Equipment: 1. Rimmed baking sheet lined with parchment paper
2. Large skillet for the onions
3. Medium skillet for the mushrooms
4. Rolling pin (keep the pastry cold)
5. Sharp chef’s knife and cutting board — you’ll use both a lot
6. Box grater for the smoked gruyere
7. Wooden spoon or silicone spatula for stirring
8. Small bowl and pastry brush for the egg wash
9. Wire cooling rack and oven mitts for handling hot trays

Ingredients

2 sheets frozen puff pastry, thawed (about 17 x 11 inches each)
3 medium yellow onions, thinly sliced, about 4 cups
2 tablespoons unsalted butter
1 tablespoon olive oil
1 teaspoon granulated sugar
1/2 teaspoon kosher salt, plus more for seasoning
8 ounces cremini or baby bella mushrooms, sliced
1 tablespoon unsalted butter for mushrooms
6 ounces smoked applewood gruyere, grated
1 large egg, beaten (for egg wash)
1 tablespoon Dijon mustard (optional but good)
1 teaspoon fresh thyme leaves, chopped, or 1/2 teaspoon dried thyme
Freshly ground black pepper, to taste

Directions

Preheat oven to 400°F (200°C) and line a baking sheet with parchment, keep a rack in the middle of the oven. Make sure the puff pastry is thawed and still cold before you roll it out.
Heat 2 tablespoons unsalted butter and 1 tablespoon olive oil in a large skillet over medium low heat. Add the thinly sliced onions, 1 teaspoon granulated sugar and 1/2 teaspoon kosher salt and cook low and slow, stirring every few minutes, until deeply browned and sweet, about 25 to 35 minutes. If they start to stick, add one to two tablespoons water to deglaze the pan. Set onions aside.
In a separate skillet melt 1 tablespoon unsalted butter over medium high heat. Add the sliced mushrooms in a single layer, salt lightly and let them brown without crowding. Stir occasionally until the mushroom liquid has evaporated and they are golden, about 6 to 8 minutes. Stir in the thyme and some freshly ground black pepper, then remove from heat.
Grate the 6 ounces smoked applewood gruyere while cold, it shreds better that way and melts nicely later.
Lightly flour your work surface if needed and roll each puff pastry sheet gently to even it out, keep it cold. If you like a little zip spread about 1 tablespoon Dijon mustard across each sheet, this is optional but good.
Cut each pastry sheet into roughly 2 inch squares (you can do bigger if you want fewer bites). Place squares on the prepared baking sheet about an inch apart. Spoon a small mound of caramelized onions onto each square, top with a few mushrooms, and sprinkle grated gruyere evenly so each bite gets cheese.
Either fold opposing corners up to make little parcels or just leave them as open tarts, either way press edges lightly to seal if folded. Brush each pastry generously with the beaten egg for a shiny golden finish.
Bake on the middle rack until the pastry is puffed and deep golden, about 12 to 16 minutes. Watch closely near the end because ovens vary.
Let cool a few minutes on a wire rack, then finish with a few extra thyme leaves and more freshly ground black pepper to taste. Serve warm.
Make ahead tip: you can assemble these and refrigerate up to 24 hours or freeze tray first then transfer to a bag. Bake from refrigerated add a few minutes, bake from frozen add about 4 to 6 minutes and check for doneness.

Notes

Below you’ll find my best estimate of this recipe’s nutrition facts. Treat the numbers as a guide rather than a rule—great food should nourish both body and spirit. Figures are approximate, and the website owner assumes no liability for any inaccuracies in this recipe.