1. Preheat the oven. Line two 23cm cake tins with baking paper and spray well with non-stick cooking spray. Beat the eggs and sugar together on high speed until very light and thick – at least 10 minutes with an electric mixer.
2. Sift the flour and baking powder twice. Also mix the butter, water and vanilla. Mix the wet and the sifted dry ingredients into the beaten egg mixture using a folding action: use a thin metal spoon or flexible spatula and fold the ingredients together until just combined. The flour should be just mixed in and not overworked, otherwise the cake will be too dense.