Substitute the same volume of oil for butter - make sure butter is not liquid but room temp and soft (it’s very important that the butter be allowed to fully melt while only in the oven otherwise it’ll just pool all at the bottom of the pan and it gets gross)
Add another egg yolk
This takes a box mix from eh to absolutely phenomenal. The box mixes are the way to go since they’re premeasured, they have the perfect ratios of flour, sugar, leaveners, and they’re sized for normal cake pans.
Substitute the water with milk
Substitute the same volume of oil for butter - make sure butter is not liquid but room temp and soft (it’s very important that the butter be allowed to fully melt while only in the oven otherwise it’ll just pool all at the bottom of the pan and it gets gross)
Add another egg yolk
This takes a box mix from eh to absolutely phenomenal. The box mixes are the way to go since they’re premeasured, they have the perfect ratios of flour, sugar, leaveners, and they’re sized for normal cake pans.