A couple of months ago I made a cake using sunflower oil instead of the usual butter.  The ingredients were oil, sugar, flour, eggs(our own from extremely happy and cosseted hens) baking powder and chopped apples.  It worked well and the tangy taste of the chopped cooking apples (from those we had stored) contrasted with the sweet sponge.  Having run out of apples I decided to make the cake with chopped rhubarb today.  It is just as delicious and we won’t run out of rhubarb until we harvest the apples in the late summer and autumn.  It’s a matter of make do with what we have and adapt the recipes accordingly.