Can I substitute olive oil for butter in Nigella's Lemon Polenta Cake? If so, how much?
In some circumstances oil can be substituted for butter in cakes but this has to be done very carefully. Usually it will work in a cake that is made using melted butter, and you need to substitute the butter with a combination of oil and another dairy ingredient, as using the same amount of oil for butter can result in a greasy cake.
In the Lemon Polenta Cake (from Kitchen and on the Nigella website) the butter is creamed with sugar before the other ingredients are added. This incorporates air which is important for the cake's texture and also helps to dissolve the sugar in the mixture. Unfotunately this means that it would be very difficult to replace the butter with oil.
If you would like to make a cake using oil that is gluten free then we would suggest trying Nigella's Chocolate Olive Oil Cake (from Nigellissima and on the Nigella website).