How do I keep cake from collapsing when adding lemon juice?
I think your fat-to-flour ratio for that kind of flour might be too high. Cake flour can't handle a lot of fat. As another answer suggested, try a higher protein flour--start with all-purpose (AP) flour and, if that isn't enough, use bread flour but remember to barely stir it together or you will make a mess. I would mix everything together except the flour first, then carefully stir it in.