For the yeast dough, put the flour in a suitable bowl and make a hollow in the center. Crumble the yeast, stir with 1 teaspoon of sugar and the lukewarm milk (not hot!) and pour into the hollow.
Stir the yeast milk with a little bit of flour to a thin liquid dampfl (than stir only a part of the flour in the baking bowl) and let it rise with closed lid in a warm place for about 20 min until the dampfl bubbles. Rinse the lemon hot, dry it and grate the peel. Prepare a smooth dough with the remaining ingredients and the sugar. Dust the dough with a tiny bit of flour and let it rise to double in a warm place with the lid closed. Grease a roasting pan with butter. Rinse and dry the plums, cut them open, remove the seeds and fill each with a sugar cube.
Dust the surface with flour, roll out the dough on it in about 5mm thin and cut 12 pieces. Cover the plums evenly with dough and put them in the roaster (seal side down) Cover and let rise in a warm place in about 20 minutes.
Preheat the oven to 200 degrees.
Bake the booklets in the middle of the oven for about 25 min. Mix cinnamon and sugar. Take out the Buchteln and brush with MIlch and sprinkle with cinnamon sugar. Serve warm or lukewarm.