In a bowl beat the butter with an electric whisk together with the sugar until the mixture is light and fluffy. Add the eggs, one by one,the grated lemon zest, the vanilla seeds and the milk. Continue to beat and stir in the sifted flour and baking powder. Turn until combined.
Pour the mixture into 12 buttered and floured muffin molds filling them 3/4 full. Bake for 20-25 minutes at 180 °, checking the cooking with a toothpick. Let them cool completely before glazing.
Now prepare the frosting in a bowl, beat the soft butterwith an electric mixer at medium speed together with half the icing sugar, thevanilla seeds and the milk. Continue to whip adding little by little the remaining icing sugar. You will need to get a smooth and thick cream.
Transfer the icing into a pastry bag with a 15 mm star nozzle and decorate the cupcakes. Serve immediately.