Hi, I wanted ask whether or not one can use vegetable oil instead of butter in Nigella's Cherry Almond Loaf cake. And if so in how much quantity? Thanks.
Nigella's Cherry Almond Loaf Cake (from Domestic Goddess) is a fairly dense sponge cake, enriched with ground almonds (almond meal). Sometimes it is possible to substitute butter for oil in a cake, but these substitutions are very recipe specific and unfortunately in this case we would not advise using oil.
One reason for not using oil is that this cake is made by creaming butter and sugar together, then beating in the eggs. The creaming incorporates some air into the mixture and if you use oil you will not be able to beat any air into the mixture. The eggs are gradulaay added to the butter and sugar and this gives a very special chemical structure known as an "emulsion". If you use oil it is more difficult to get the eggs incorporated properly and the resulting mixture will be slightly curdled and could lead to a heavy, greasy cake.
In addition, oil contains pretty much all fat whereas butter contains up to 80% fat and around 20% water and milk solids. If you use oil instead of butter then the fat content will be too high and again the cake could end up being too greasy. The milk solids in the butter also add to the flavour and if you switch to oil you may find that the cake lacks some depth of flavour.