Work 125g butter and 125g of sugar together in a bowl to obtain a creamy texture. Add vanilla extract, 3 eggs, salt and lemon zest.
Separately, mix 250g of flour with 1 teaspoon of baking powder and add this to the previous mixture, slowly adding milk until you get a soft dough. Spoon out the mixture into muffin cases and sprinkle two diced apples on top. Bake in a pre-heated oven at 180 degrees for 20 minutes. Before serving, sprinkle with icing sugar.