1 (17 1/4 oz.) package frozen puff pastry sheets, thawed
1 large egg
1/3 cup raspberry jam
3 1/2 oz fine-quality mild chocolate, finely chopped
Put oven rack in upper and lower thirds of oven and preheat oven to 425 degrees F.
Line 2 large baking sheets with parchment paper. Roll out 1 puff pastry sheet into a 12 inch square on a lightly floured surface with a floured rolling pin, then brush off excess flour from both sides. Cut into 16 squares.
Whisk together egg and a pinch of salt. Place 1/2 teaspoon jam and 1 teaspoon chocolate in center of each square, then brush edges of squares with some of the beaten egg. Fold each square in half to form a triangle, pressing edges to seal. Brush tops of pastries with some of remaining egg and transfer to a lined baking sheet. Chill on sheet while making 16 more pastries in same manner, transferring to second baking sheet.
Bake pastries, switching position of sheets halfway through baking, until golden and cooled through, about 20 minutes. Cool on sheets on racks 5 minutes. Serve warm.