According to Guy, there isn't one single answer to the question, but a great deal of nuance. "It depends on the style of cookie you're making and the texture you're looking for," she explains. "Butter is usually the go-to choice (solid or melted) because it adds so much flavor." Outside of flavor, Guy revealed that butter can do one other thing: "Solid butter should be the go-to choice for structure." You see, when it's creamed, it adds air to the dough and forms a stabilizing network with the fats and sugar, giving your cookies their shape and texture.