Cocoa powder acts like flour. If you want to add cocoa powder to a recipe that doesn't call for it, use less flour on a 1:1 ratio. For example, if your recipe calls for 2 cups flour and you want to add 1/2 cup cocoa powder, only use 1 1/2 cups flour. Otherwise, the cocoa powder may cause your cookie dough to be dry. Note: If your recipe already included cocoa powder, use the amount of flour and cocoa powder that is listed. If you're worried about rolling out cookie dough using cocoa instead of flour, you'll find that it isn't a problem. The cocoa powder acts like flour (only it's a little messier!).