Put the flour in a bowl. Put the egg yolk, butter, milk, sugar and a little cinnamon on top and mix well with the mixer. Then add the rum and the mineral water and mix again briefly.
Now let the dough rest a little. In the meantime, peel the apple, remove the core and cut into small pieces. In another bowl, beat the egg whites into snow. Then lift the snow under the dough.
Now heat some oil in the pan. First fry the apple pieces a little. Then add the dough and repeatedly crush and stir so that small crumbs are formed.
Decorate the finished Schmarrn on the plate with sugar, cinnamon, grated hazelnuts and apple pieces according to taste.
This dish is suitable as a main course as well as a dessert. However, the quantities given here refer to a main course. As a dessert, you can simply make smaller portions (about half of the main course).
In general, one can say: Use less sugar for the main course, as a dessert it can be a little sweeter.