For the dampfl, first dissolve the yeast and about 1/3 of the sugar in a little warm milk, stir in 2 tablespoons of flour, cover the whole thing with some more flour and leave everything in a warm place until cracks form on the surface.
In a bowl, beat the dampfl, melted butter, remaining milk, remaining sugar, egg and yolks, a pinch of salt, vanilla sugar and lemon zest, and remaining flour using a wooden spoon or food processor to make a smooth yeast dough.
When the dough is smooth enough to be easily removed from the spoon, let it rise again in a warm place until it has doubled in volume.
Then roll out the dough on a floured work surface, not too thin, and divide it into square pieces.
Mix the powidl well with a strong shot of rum and place a dollop of it in the center of each piece of dough.
Fold the ends of the dough over each other and press down well. Grease a large ovenproof dish with butter, place the Buchteln in the dish with the pressed ends facing downwards, brushing each one thoroughly with melted butter.
Now let the Buchteln rise once again and in the meantime preheat the oven to 180 °C.
Then bake for about 20 to 30 minutes until golden brown. Turn out the cooled Buchteln and sprinkle with powdered sugar.
Preparation Tip:
For variety, the Buchteln can also be filled with a poppy seed or curd cheese mixture.