Caramelized Onion Puff Pastry Bites with Gruyere and Mushrooms

Why You’ll Love This Recipe

I like this recipe because it takes simple ingredients and turns them into a party-worthy appetizer. The caramelized onions bring sweetness, the gruyere adds nuttiness, and the mushrooms deepen the flavor. Wrapped in golden puff pastry, each bite is perfectly crisp and cheesy.

Ingredients

(Note: All ingredient amounts are listed in the recipe card below.)
4 tablespoons salted butter, divided
2 tablespoons vegetable oil, divided
5-6 ounces crimini or button mushrooms, sliced
2 medium yellow onions, thinly sliced
1/4 teaspoon dried thyme
1 tablespoon sugar
1 1/2 tablespoon balsamic vinegar
1/4 teaspoon garlic powder
salt and pepper, to taste
4 ounces grated gruyere cheese (I used applewood smoked gruyere)
1 package (1 pound) frozen puff pastry, thawed
1 egg, lightly beaten

Directions

1. I melt 2 tablespoons of butter with 1 tablespoon oil in a large skillet over medium heat, then add the onions, thyme, sugar, salt, and pepper. I cook slowly for 20–25 minutes, stirring often, until the onions are golden and caramelized.
2. I stir in the balsamic vinegar and cook for another 2 minutes. I remove the onions from the pan and set aside.
3. In the same skillet, I melt the remaining butter with the remaining oil, then sauté the mushrooms with garlic powder, salt, and pepper until browned and tender.
4. I preheat the oven to 400°F (200°C) and line a baking sheet with parchment paper.
5. I roll out the puff pastry on a floured surface and cut it into squares (about 2 inches).
6. I place the pastry squares on the baking sheet and top each with a spoonful of onions, a few mushrooms, and some grated gruyere.
7. I fold the corners slightly inward, brush the pastry edges with beaten egg, and bake for 15–18 minutes until golden and puffed.
8. I serve them warm, straight from the oven.

Servings and Timing

This recipe makes about 24 puff pastry bites. It takes me 25 minutes to prep and 20 minutes to bake, so they’re ready in around 45 minutes.

Variations

Sometimes I use brie or fontina instead of gruyere for a creamier filling. I also like to add fresh herbs such as rosemary or parsley for extra freshness. For a sweeter twist, I stir a little fig jam into the caramelized onions before assembling.

Storage/Reheating

I store leftover bites in an airtight container in the refrigerator for up to 2 days. To reheat, I place them in a 350°F (175°C) oven for about 8 minutes until crisp again. I avoid microwaving since it makes the pastry soggy.

FAQs

Can I make these ahead of time?

Yes, I prepare the filling in advance and assemble just before baking.

Can I freeze them?

Yes, I freeze unbaked assembled bites and bake directly from frozen, adding a few extra minutes.

Do I need to thaw the puff pastry completely?

Yes, it should be thawed but still cold for easy handling.

Can I use store-bought caramelized onions?

Yes, but I prefer making them fresh for the best flavor.

What mushrooms work best?

I usually use crimini, but shiitake or portobello also work well.

Can I make them bigger?

Yes, I cut larger pastry squares and serve them as hand pies instead of bites.

How do I keep the pastry from getting soggy?

I drain any excess liquid from the onions and mushrooms before assembling.

Can I serve them cold?

They taste best warm, when the cheese is melty and the pastry is crisp.

Can I make them vegetarian?

They already are, but I can use plant-based puff pastry if needed.

Conclusion

I love making these caramelized onion puff pastry bites with gruyere and mushrooms because they’re elegant, flavorful, and always a hit at parties. With flaky pastry, savory filling, and melty cheese, they’re the kind of appetizer that disappears quickly from the table.

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