For the dough, stir together the butter, sugar and vanilla sugar until foamy, add the eggs while stirring. Add a few drops of lemon flavor. Sift the flour if possible and gradually add it together with the biscuit spice and baking powder. Continue stirring until the dough is smooth (approx. 3 minutes).
Peel and core the apples and cut into pieces the size of a thumbnail. Mix the apple pieces into the batter. Divide the batter into 12 muffin cases.
For the crusty crust, put the butter, vanilla sugar, sugar, flour and biscuit spices in a bowl and mix into small crumbles by hand. Then pour this evenly over the muffin batter. Bake the muffins for about 45 minutes in a preheated oven at 170 ° C (top / bottom heat).
Tip: Put the leftover crumble with another sliced apple in a small baking dish and bake for about 30 minutes. Makes a delicious crumble that tastes best warm with vanilla ice cream.