Prepare the Cinnamon Sugar: In a small bowl, whisk together the granulated sugar and cinnamon until they're evenly combined.
Unfold the Puff Pastry: Gently unfold one sheet of the thawed puff pastry onto a lightly floured surface.
Brush with butter: Take the melted butter and brush it on the surface of the puff pastry.
Sprinkle with Cinnamon Sugar: Sprinkle the cinnamon-sugar mixture evenly over the pastry.
Cut into Triangles: Cut the pastry sheet in half lengthwise, then cut each half into triangles (6-8 per sheet).
Roll into Croissants: Starting at the wide end of each triangle, gently roll it up towards the pointed end.
Place on Baking Sheet: Place rolled croissants on a parchment-lined baking sheet, leaving space between.
Apply Egg Wash: Brush the top of each croissant with the beaten egg.
Sprinkle with Turbinado Sugar (Optional): If using, sprinkle turbinado sugar over the egg-washed croissants.
Bake: Bake at 375°F (190°C) for 15-20 minutes, until golden brown and puffed.
Cool Slightly: Let croissants cool on the baking sheet before transferring to a wire rack to cool completely.