Preheat oven to 180 degrees Celsius. Grease a loaf pan with soft butter and line the bottom of the pan with parchment paper. Melt the butter and add the milk to it, mix and set aside
Sift the flour and baking powder and set aside. Using an electric hand mixer beat eggs and sugar for 8 minutes until it's doubled in volume
Mix in lemon zest and vanilla essence
Add the flour and the melted butter and give it a quick mix ith the electric mixer until almost combined. Add the milk and give it another quick mix. If there's little bits of flour visible that's ok. Do not over mix
Pour the batter into the loaf pan and bake for about 40-45 minutes or until a toothpick inserted in the center comes out clean. If the cake it getting brown too soon, cover with a piece of foil
Cool cake on a cooling rack and cut only when completely cool