Preheat the oven to 350°F (175°C) and line a baking sheet with parchment paper.
In a medium bowl, whisk together melted butter, sugar, eggs, and vanilla extract until smooth.
Sift in cocoa powder, flour, salt, and baking powder, then stir until just combined.
Fold in chocolate chips if desired.
Unroll the crescent roll dough and separate it into triangles along perforations.
Place a tablespoon of the brownie batter at the wide end of each triangle.
Roll each triangle from the wide end to the pointed end, enclosing the batter inside.
Arrange croissants on the baking sheet with the pointed end facing down.
Bake for 12 to 15 minutes until golden brown and puffed.
Allow croissants to cool slightly before serving warm.