Make the cookie dough filling: cream the butter and sugars until light and fluffy. Add the egg and vanilla, mixing thoroughly. Gradually incorporate the flour and salt until a smooth dough forms, then fold in the chocolate chips.

Roll the chilled croissant dough into thin, even triangles.

Spread the cookie dough filling evenly across each triangle, then roll up into a classic croissant shape, stretching the corners gently.

Space the croissants evenly on a baking sheet and brush with the egg wash for a golden, glossy finish.

Preheat the oven to 375-400°F. Bake for 12-15 minutes, until golden brown with crispy edges and rotating the sheet halfway through for even browning.