From: LOL Foodie
1 sheet of frozen puff pastry dough, thawed
2 tbs butter
half of a large onion
2 apples (Granny Smith or another tart variety)
1/4 tsp freshly ground black pepper
1/3c fontina cheese, shredded
1 tsp minced fresh thyme
1/2 tsp salt
Begin with prep work. Slice/chop the onion very thinly. Peel and core the apple, and chop it into pieces approximately the same size as the onion.
Heat the butter in a saute pan over medium. Once it’s melted, add the onions and 1/4 tsp of salt. Saute onions until soft, about 5 minutes.
Add the apples, and reduce the heat to low. Cook over low for about 30 minutes. The onions should be nice and caramelized, and lightly browned. Stir in the pepper and remaining salt. Remove from heat and let cool.
Preheat the oven to 375 degrees F, and line a baking sheet with parchment paper.
Unwrap and unfold the puff pastry dough. Slice along the folds already present in the dough, creating 3 even “strips” of dough. Cut each strip into 3 squares, then slice diagonally through each square to create 2 triangles. This should result in 18 triangles from the entire sheet of dough.
Place each dough triangle on your prepared baking sheet, without touching.
Spoon about 2 teaspoons of the onion-apple mixture onto each dough triangle. Sprinkle some of the grated fontina cheese on top. Sprinkle thyme on top of the cheese.
Bake for 15 to 20 minutes, and serve warm!
Make-ahead note: You can caramelize the onions-apple mixture and store it in the fridge up to two days beforehand. You can assemble the tarts one day before you serve them, and just store in the fridge, wrapped in cling wrap or foil on a baking sheet. Just pop them into the oven when you are ready!