To make the buckwheat apple cake recipe dairy-free, how much olive oil is needed to replace the butter?
Generally speaking you'll want to use about 75% as much oil as butter in a baking recipe. The problem with this recipe is it calls for creaming the butter with the sugar, and when you're using liquid oils that part can be problematic. In order to make sure you don't sacrifice texture, do NOT skip the step where you separate the yolks from the whites! Beating the whites and then gently folding it in will be absolutely necessary with this recipe in order to not end up with a dense cake.