01 - Preheat oven to 400°F. Line a baking sheet with parchment paper to prevent sticking and ensure easy cleanup.
02 - Unroll puff pastry on a lightly floured surface. Using a sharp knife or pizza cutter, divide into 8 equal rectangles, approximately 3x4 inches each.
03 - In a small bowl, combine dulce de leche with optional ground cinnamon. Stir until thoroughly incorporated and smooth.
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 create a tight seal and prevent filling leakage during baking.
05 - Transfer filled pastries to prepared baking sheet, leaving 1 inch of space between each. Brush tops generously with beaten egg using a pastry brush to promote golden browning.
06 - Combine granulated sugar and ground cinnamon in a small bowl. Sprinkle mixture evenly over the tops of all pastries.
07 - Bake for 18-20 minutes until pastries are puffed, golden brown, and cooked through. Rotate baking sheet halfway through cooking time for even browning.
08 - Allow pastries to cool on baking sheet for 5 minutes before transferring. Serve warm for gooey filling or at room temperature. Best enjoyed within 4 hours of baking.