01 - Preheat oven to 400°F. Line a baking sheet with parchment paper for easy cleanup and to prevent sticking.
02 - Unroll puff pastry on lightly floured surface. Cut into 8 equal rectangles using a sharp knife or pastry cutter.
03 - Combine dulce de leche with cinnamon in small bowl if desired. Mix thoroughly until well blended.
04 - Place generous tablespoon of dulce de leche mixture in center of each pastry rectangle. Fold pastry over to form squares or triangles. Press edges firmly with fork to seal completely.
05 - Arrange sealed pastries on prepared baking sheet. Brush tops generously with beaten egg for golden color.
06 - Combine sugar and cinnamon in small bowl. Sprinkle evenly over egg-washed pastries.
07 - Bake for 18-20 minutes until pastries are puffed and golden brown. Watch closely during final minutes to prevent over-browning.
08 - Allow pastries to cool for 5 minutes on baking sheet. Serve warm or at room temperature for best texture.