This may sound a little adventurous, but you won't taste the difference: Switch out half of the butter in a cookie recipe for mashed avocado. This simple change will reduce fat content by 40% and cut the number of calories by nearly as much. You'll still get the creaminess of butter and the fatty taste, but this substitution knocks out some of the saturated fat in favor of the belly-flattening monounsaturated kind.