Hello! Anyone know the answer? Boys and I are very keen to cook Nigella's Autumnal cake today as it looks so yum but we couldn't find cream of tartar- of which the recipe calls for 1/4 teaspoon- in Sainsbo's. Can we use something else? Am assuming it's some kind of raising agent? Would bicarb or baking powder or anything else I might have in the cupboard do or should I just give up the whole plan? V grateful for any thoughts.