Preheat oven to 375°F (190°C). Line a baking sheet with parchment paper.

Gently unfold one sheet of the thawed puff pastry on a lightly floured surface.

Use a sharp knife or a pizza cutter to cut the pastry sheet into large triangles.

Place a small spoonful of chocolate chips at the wide end of each triangle.

Starting at the wide end, carefully roll up each triangle towards the point. Gently curve the ends inward to create that classic croissant shape.

Place the rolled croissants on the prepared baking sheet, leaving a little space between each one.

In a small bowl, whisk together the beaten egg and water. Brush the tops of the croissants with the egg wash.

If using coarse sugar, sprinkle it over the egg-washed croissants now.

Bake for 15-20 minutes, or until the croissants are golden brown and puffed up.

Let the croissants cool on the baking sheet for a few minutes before serving.