For this simple sponge cake, choose your favorite filling - we used lemon curd and whipped cream, but you could also use jam. It's ideal for afternoon tea.
Preheat the oven to 180°C/160°C fan/gas 4 and butter and line two 20cm spring-form cake tins with baking parchment.
Beat the butter and sugar together with an electric mixer until pale and creamy. Crack the eggs into the bowl one at a time, whisking well after each addition and scraping down the sides of the bowl. Combine the lemon zest, vanilla, flour, milk, and a bit of salt in a mixing bowl. Whisk together until just blended, then divide into the two muffin pans.
Bake for 25-30 minutes in the center of the oven, or until a skewer inserted in the center of each cake comes out clean. Remove the cakes from the tins after 10 minutes and cool fully on a wire rack. Fill in the blanks as desired. A generous dollop of lemon curd and some fresh cream, then dusted with icing sugar, is my particular favorite. It will last 3 days in the fridge.