Preheat oven to 350°F. Line a baking sheet with parchment paper.
Flour the working surface and spread the puff pastry sheets flat on it.
Use a pizza cutter and cut it into triangles. Each pastry will give about 4-5 triangles.
Now place the chocolate bar or chips on the long end of the triangle and roll up till if forms a croissant shape.
Hold the 2 ends and gently bend so it slightly forms a "C" shape or crescent shape.
Repeat the process with the rest of the puff pastry.
In a small bowl, whisk the egg with 1 tablespoon water.
Place rolled croissants on the lined sheet then brush the egg mixture generously all over the top of the rolls.
Bake for 30 minutes until the croissants puff, and are light gold and crunchy.
Serve immediately.
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Notes
Use a sharp knife or pizza cutter to cut the puff pastry into triangles. You can cut the dough into smaller triangles to make mini croissants too.
If you're making mini croissants, keep in mind that they will need less time to cook.
If you're making these for a crowd and want them to look extra fancy, you can top them with a light dusting of powdered sugar or a drizzle of Nutella or chocolate sauce right before you serve.
If you want to make these egg-free, brush the prepared croissants with melted butter (or vegan butter if you want them to be vegan).
For a deeper golden brown color and a rich flavor, use only egg yolk for the egg wash.
If your puff pastry dough is thick, you may want to roll it into a thinner sheet- about ⅛ inch in thickness.