Adding bean puree to brownies or cake (or really anything calling for oil!): Simply use the same amount of bean puree that your recipe calls for oil. For example, if your brownie recipe calls for 1/3 c. oil, you would instead use 1/3 c. bean puree. Try to pick a color that will match what you are doing (so, you could do white beans and black beans in a chocolate cake but I wouldn’t do black beans in a white cake=make sense? Good!)
Home Cooked Beans: Take cooked beans (reserve the cooking water) and blend in your blender with enough water to create a thick paste. (Basically enough water to make all the beans turn into a puree. If you need to see how to cook beans, read below.
Canned Beans: Dump entire contents of can (beans and water) into a blender and blend until it is a thick paste.