Hoping someone can help. I want to change my cake recipe a little and instead of using 424g butter I want to use half that so 212g butter and instead add oil to make up the rest. How much oil would I add. Do I just add the remainder 212g oil to makeup the 424g or do I use a different amount of oil. I am hoping to replace some of the better with vegetable oil. My recipe also includes 1 1/4 cup butter milk and whole Milk combined. Thank you 

it will change up everything in the recipe -- what i would recommend is to make a half recipe or a third or quarter -- whatever fraction of the recipe you can make with one egg -- and use the ratio you said half & half --

if it was me i'd find another recipe altogether

it may work great -- idk -- and if you want to reply pls start a new thread 

I've made cakes with butter and I've made cakes with oil, but never tried to substitute one for the other.  -K8memphis' suggestion is about the only way to find out how it will work.

I make a ton of quick bread recipes & have often used one for the other— I think I have even use both in one recipe but not sure now.   Quick breads are similar to cakes but a bit more dense/heavier.    

What is the reason for wanting to use both?