01 - Preheat oven to 400°F. Line a baking sheet with parchment paper and set aside.
02 - Unroll puff pastry on a lightly floured surface. Cut into 8 equal rectangles.
03 - In a small bowl, mix dulce de leche with cinnamon if using.
04 - Place 1 generous tablespoon of dulce de leche mixture in the center of each pastry rectangle. Fold pastry over to form squares or triangles. Press edges firmly with a fork to seal.
05 - Arrange pastries on prepared baking sheet. Brush tops generously with beaten egg.
06 - Combine sugar and cinnamon in a small bowl. Sprinkle mixture evenly over the egg-washed pastries.
07 - Bake for 18-20 minutes until pastries are golden brown and puffed.
08 - Cool slightly on baking sheet. Serve warm or at room temperature.