1 sheet frozen puff pastry, thawed according to package directions
All-purpose flour, for dusting counter
1 cup semisweet mini chocolate chips
1/2 cup good-quality chocolate-hazelnut spread
1 egg, beaten with 1 teaspoon water
Preheat the oven to 375 degrees F. Line a baking sheet with parchment paper.
Roll out the puff pastry on a lightly floured work surface to make a 12-inch square. Using a chef's knife or pizza cutter, cut into four equal squares. Brush two edges of each square with egg wash.
Stir the chocolate chips into the chocolate-hazelnut spread, then divide among the squares, landing it in the centers. Fold the pastry over to make triangles, and press the edges to seal. Brush the tops of turnovers with more egg wash.
Transfer the turnovers to the prepared baking sheet. Bake until the pastry is golden brown and the chocolate has melted, about 15 minutes. Cool on a baking rack for 10 minutes. Serve warm.