Summarize this article:

Various flour types can be used to flour the pan, but the rule of thumb is to use the flour that the recipe called for. This way you won't be altering the taste or composition of the batter. Flour is tasteless, but it can leave a white residue on baked goods, especially if they are chocolate ones. For chocolate cakes, muffins, or any baked good that has cocoa powder in it, set aside some cocoa powder in place of flour.

Summary:
Set aside some flour that is already used in your recipe. Choose cocoa powder instead of flour for chocolate baked goods.