These cheesy mushroom tartlets are the perfect appetizer for holiday parties - made with onions, mushrooms and cheese on top of a buttery flaky mini pastry!
In a large pan over medium heat, heat 2 tablespoons olive oil. Add the onions and cook for 15 minutes, stirring occasionally until soft and golden. Stir in the brown sugar and salt and add the mushrooms. Cook together the mushrooms are caramelized, about 5-7 minutes. Stir in the garlic and thyme and cook together until fragrant, about 1-2 more minutes. Turn off the heat and set aside.
Unfold the pastry sheet on a lightly floured surface. Roll the pastry sheet into an 18x9-inch rectangle. Cut into 18 (3-inch) squares or circles as I show. Press the pastry squares into 18 muffin-pan cups. Brush the edges of the pastries with the egg. Prick the centers of the pastries with a fork.
Spoon about 2 tablespoons of the onion and mushroom mixture into each square. Top with about ½ tablespoon of the cheese. Makes 24 - 36.
Bake the tartlets until they’re golden brown, about 18-20 minutes. Remove the pastries from the muffin-pans and cool on wire racks for 10 minutes. Garnish with fresh thyme or parsley, if desired.
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Notes
Storage: Store any leftovers in an airtight container. They will last up to 4 days in the fridge. To reheat, place in the microwave for 30 seconds or in the oven at 350°F for 5 minutes.Make ahead: You can make the mixture up to 24 hours ahead of time and keep them in the fridge. However, don't assemble on the puff pastry until you're ready to bake them to avoid the tartlets become soggy.Freezer Instructions: You can freeze the mushroom mixture in a freezer safe container or freezer bag for up to 3 months. Thaw in the fridge overnight, then add to the puff pastry before baking.