Put the sugar and lemon zest in a blender or food processor. Blend until the lemon zest is fine. Add this mixture to the softened butter. Beat with a mixer on medium until fluffy. This should take about 5 minutes. Add the eggs to the sugar and butter one at a time, beating well after adding each one. Add the water, lemon juice, and vanilla. In a different bowl, use a whisk to mix the flour, baking powder, and salt. Add half of the flour mixture to the rest of the ingredients. Mix on low. Then add the rest of the flour mixture. Now beat at medium speed until the cake batter becomes shiny. The mixture should also turn a white color. Do not skip this step or reduce the mixing time. The longer you mix the batter, the more air bubbles you create. This is what makes sponge cake recipes light and fluffy. This step of the sponge cake recipe should take about 15 minutes. Pour sponge cake batter into two round cake pans that have been greased with shortening well and liberally floured. If they haven't been greased and floured thoroughly, your sponge cake recipe will stick to the cake pans. Bake lemon sponge cake in a preheated 350 degrees Fahrenheit oven for approximately 25-30 minutes. The sponge cake should pull gently from the sides. It will be golden in color and spongy to the touch. It should spring back when touched. To be sure the sponge cake is done, test the center with a toothpick and see if it comes out clean. Do not open the oven while the sponge cake is baking. Remove the lemon sponge cake from the oven and let cool on a wire rack for about 10-15 minutes before removing the cake from the cake pans. Let the sponge cake cool completely before frosting it. A lemon glaze would work well with this basic sponge cake recipe. Of course, frosting a sponge cake is optional. Plain sponge cake recipes are delicious by themselves.Victoria Sponge cake 125g butter 125g caster sugar 2 eggs 125g self-raising flour, sifted 2 tbsp milk Beat the butter and sugar together till it's creamy, add the beaten eggs, gradually add the flour and fold into the mixture. Add milk. Spoon into 2 x 8" tins. Bake at about 190 for about 15 mins or until golden and not wobbly!