Preheat oven to 400°F.,

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 until 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 18×9-inch rectangle. Cut into 18 (3-inch) squares or circles. 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 – ,

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.