For the sweet pastry crust, beat the room temperature butter with the sugar, vanilla sugar, eggs and lemon zest. Add the flour, baking powder, rum and a pinch of salt and knead the mixture to a firm consistency. Let the pastry pat rest for about 30 minutes and then roll it out into a rectangle. For the filling, peel, core and slice the apples. Add the apples to the other ingredients and spread the filling over the pastry crust. Fold the strudel and bake in a preheated oven at 165 °C for about 50 minutes. Cut the strudel into slices, arrange on plates and garnish with vanilla sauce and strawberries.