For every 3 tablespoons of cocoa powder required, you can use 1 ounce of melted unsweetened chocolate, but reduce the fat in your recipe, as the chocolate contains more fat than cocoa powder. You can also use Dutch-process cocoa, but you'll need to boost the acidity in your recipe by adding 1/8 of a teaspoon of cream of tartar, lemon juice, or white vinegar.

Melted unsweetened or semi-sweetened chocolate chips are great substitutes, too. However, semi-sweet chips contain added sugar, so reduce the amount of granulated sugar or other sweeteners you add — and also compensate for any cocoa butter in the chocolate by reducing the butter or shortening.

As for a non-cocoa substitute, use carob powder measure for measure to the cocoa powder, but only as a last resort. Cocoa mix only has a small amount of cocoa powder in it, so measure for measure, you will be adding less cocoa powder to your recipe, as well as the addition of everything else in the cocoa mix, and it can be hard to figure out exactly how much to add.