Quickly mix the not too cold butter with the sugar, the lemon zest and vanilla sugar in a bowl to form a homogeneous mass (until you can’t see any more pieces of butter). Add the egg and the milk, then mix in the flour and baking powder and knead to form a dough. Leave the dough to rest for 1/2 an hour before use. Peel the apples and remove the seeds, cut into small slices and mix with the sugar, breadcrumbs, sultanas, pine nuts, rum, vanilla sugar, cinnamon and lemon zest. Pre-heat the oven. Roll out the dough on a floured pastry board to 40 x 20 cm and place on a butter greased baking sheet. Place the apple mixture on the dough and fold the dough over it. Brush the strudel with the whisked egg, decorate with leftover strips of dough and bake in the oven. Sprinkle with icing sugar.
Baking temperature: 180 degrees
Baking time: 35 minutes