When adding eggs to butter, be sure to add them in batches, and beat each time until the eggs and butter are safely combined before adding the next time. Be sure not to rush it to avoid egg-oil separation. The butter does not need to be overbeated. The entire whipping process can be controlled in about 5 minutes (depending on the specific situation). Use 30 grams of cocoa powder instead of the same amount of flour to make chocolate-flavored butter cookies. The baking time of the cookies is short and they are easy to burn. Be sure to watch them during the last few minutes. Take them out after they are baked to your preferred coloring level.