Why do some recipes say to sift drying ingredients with cocoa powder in them, and others say to whisk?
Because it’s so fine, cocoa powder tends to lump up in the container. So you either need to sift or whisk it well to break up the lumps. It’s also a good idea to disperse the cocoa powder in other dry ingredients in recipes, especially if using a stand mixer, as the fine cocoa powder tends to easily fly out of the mixing bowl when mixing.