If you want to make an even softer and fluffier cake with a greater rise, and one that stays softer for longer, you can substitute half of the butter for a neutral-tasting oil, such as sunflower, vegetable, or canola oil. … Regular dairy butter is composed of about 80% fat, 15% water, and 5% milk solids – so when you’re swapping butter for oil, it’s not a 1:1 substitution. Instead, you need to replace the butter with 80% of oil and 15% of milk.