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Caramelized Onion Mushroom Apple Gruyere Bites

Caramelized onion mushroom apple Gruyere bites bake puff pastry squares until puffed and deep golden, with melted cheese and a savory-sweet topping. Thinly sliced onions cook slowly with mushrooms, apple, and thyme for a rich, tender filling.
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Prep Time 20 minutes
Cook Time 1 hour 2 minutes
Resting 5 minutes
Total Time 1 hour 27 minutes
Servings: 12 servings
Course: Appetizer
Cuisine: American
Calories: 260
Ingredients Equipment Method Notes

Ingredients
  

For the topping
  • 1 tbsp olive oil
  • 2 tbsp unsalted butter
  • 2 yellow onions medium, thinly sliced
  • 0.5 tsp kosher salt
  • 8 oz cremini mushrooms thinly sliced
  • 1 apple medium, cored and cut into 1/4-inch dice
  • 1 tsp thyme fresh leaves, chopped
  • 0.25 tsp black pepper
For the bites
  • 1 package (17.3 oz) frozen puff pastry 2 sheets, thawed according to package directions
  • 6 oz Gruyere cheese shredded

Equipment

  • 1 12-inch skillet
  • 2 large baking sheets

Method
 

Cook the topping
  1. Heat the olive oil and butter in a 12-inch skillet over medium-low heat.
  2. Add the onions and salt.
  3. Cook, stirring occasionally, for 30–35 minutes, until the onions are very soft and deep golden brown.
  4. Add the mushrooms.
  5. Cook for 8–10 minutes, stirring occasionally, until browned and their released liquid has evaporated.
  6. Stir in the apple, thyme, and black pepper.
  7. Cook for 2–3 minutes, until the apple just begins to soften.
  8. Remove the skillet from the heat.
Assemble and bake
  1. Heat the oven to 400°F.
  2. Line two large baking sheets with parchment paper.
  3. Cut each puff pastry sheet into 12 equal pieces (3 columns by 4 rows).
  4. Arrange the pastry pieces on the prepared sheets with space between.
  5. Score a 1/2-inch border on each piece.
  6. Dock the centers several times with a fork.
  7. Divide the Gruyere and onion mixture evenly among the pastry centers, keeping the toppings inside the scored borders.
  8. Bake for 16–20 minutes, swapping the sheets between racks and rotating them front to back halfway through, until the pastry is puffed and deep golden and the cheese is melted.
  9. Let the bites rest on the baking sheets for 5 minutes before serving.

Notes

For the best flavor, cook the onions slowly until very soft and deep golden brown. Refrigerate leftovers for up to 3 days; freeze baked bites for up to 1 month and reheat until crisp. For a dairy-free option, use dairy-free butter and cheese and check that the puff pastry is dairy-free.