Butter and line the base of a 20cm round, 18cm square or 2lb loaf tin with non-stick baking parchment, held in place with a little butter.
If using a loaf tin, take three times the length of the tin in aluminium foil, fold the upper and lower thirds inwards, producing one very long narrow foil collar. Carefully bend the foil so it sits upright and tight against the inside of the loaf tin and pinch the join together so it does not split.
Cream the butter and sugar until light and fluffy, add the eggs, one at a time and beat well till combined using an electric whisk. Beat in the sour cream till it vanishes into the mixture, then sift the flour and baking powder together and beat this through.
Spoon mixture into the tin, heat the oven to 180°C (160°C fan-assisted) and bake for 45 minutes (shallow cake) to an hour (deep loaf tin with a collar) or until a skewer inserted comes out clean.
Allow to cool and drizzle with lemon water icing.
Lemon Water Icing
Ingredients
200g Icing sugar, sifted 25ml Boiling water 50ml Freshly squeezed lemon juice Zest of a lemon, finely grated
Method
Mix all ingredients together in a bowl until smooth and pour over cake.