Be sure to use unsweetened cocoa powder in baking, not cocoa drink mix with sugar or other sweetener. My friend Mike once ran out of cocoa powder and sugar. The corner store was out of these supplies. In a desperate chocolate fit, he made brownies with what he had on hand — artificially sweetened Diet Swiss Miss Cocoa Mix. They were frankly terrible. The texture and taste were all wrong.
According to Penzeys Spices, “Natural Cocoa is strong, dark, and bittersweet, perfect for all baking.” Rich, smooth Dutch Cocoa is for drinking: it is “processed to temper the acidity of the cocoa bean”. They say that “American cooks tend to prefer the Natural Cocoa for all uses” and baking. They sell both Natural or Dutched cocoa, and even have a Cocoa Lover’s Gift Box that includes these cocoa powders plus hot cocoa mix.
When baking with cocoa powder, I often use 2/3 natural cocoa powder (unsweetened) and 1/3 Black Cocoa (Dutch-process) from King Arthur Flour. It is like dark chocolate in a powder form, and is best when combined when regular cocoa. Example, if a recipe calls for 3 T cocoa, I use 2 T natural cocoa powder and 1 T black cocoa powder. King Arthur also sells “Double-Dutch Dark Cocoa”, which is a blend of Dutch-process and black cocoas. You can buy these dark cocoas directly from King Arthur or from amazon.com.