Sift flour into a bowl and make a well in the center. Crumble yeast into the well, add 2 tablespoons of warm milk and 1 tablespoon of sugar. Dust some flour over yeast and allow to stand for about 20 minutes in a warm place. Combine egg with remaining milk, sugar and lemon zest. Add to flour and knead quickly. Cover and let rise for another 30 minutes. Divide dough into 8 equal sized pieces, form dumplings and slightly flatten. Let stand for 20 minutes. In a large pot, bring salted water to a boil. Place dumplings into slightly boiling water and cook for about 15 minutes on low heat, stirring occasionally.
Melt vanilla sugar with butter just before serving.
Remove dumplings with a slotted spoon and place into a bowl. Drizzle with vanilla butter and dust with cinnamon. Serve.