If frozen, thaw puff pastry at room temperature for 40 minutes. Preheat oven to 375F and line a baking sheet with parchment paper or a silpat liner.
Unfold the pastry (there’s no need to roll it out) and if necessary, trim the edges so they’re straight. Cut the pastry into 4 equal parts and spoon 2 TB jam onto the center of each. Lightly brush 2 edges with eggwash, and then fold over into a triangle. Lightly push edges down first with your fingers, then with the tines of a fork.
Transfer the turnovers to the prepared baking sheet. Lightly brush the tops with eggwash (you will have extra eggwash), then sprinkle a little sugar on top of each turnover. Bake about 25 minutes, or until puffed and golden.