Make the dough. In a large mixing bowl, dissolve the yeast in half of the milk and mix in a tbsp of the flour. Let rise in a warm place for 20 min. Add the rest of the milk, flour, half of the butter, sugar, eggs and lemon zest and knead a dough. Let rise for another 30 minutes. In the meantime, butter a baking dish.
Shape the Buchteln. Knead the dough again and cut into 10 (more or less) equal pieces. Flatten them into rounds and put a tsp of jam in the middle. Carefully fold them over once and close them, then fold over once more, so you get nice little packages. Dunk them in the remaining butter and place next to each other in the baking dish with the “seam” down. They can touch each other, but don’t pack to tightly. Let them rest in a warm place for another 20 minutes, while heating the oven to 305 Fahrenheit.
Bake the Buchteln for about 20 minutes, until golden brown. Before baking them, brush with the remaining butter. In the meantime, make the sauce: Put the wine, eggs, lemon juice and sugar in a bowl. Over a hot water bath, whisk vigorously for 10 minutes until everything has combined to a thick foam.
Serve sauce and Buchteln together – either while still warm or cold. Although who has the patience to wait for them to cool?