From an old cookbook, Buchteln like grandma used to make, incredibly delicious!

Activate yeast: In a small bowl, crumble the yeast and dissolve it in the lukewarm milk and water. Let it sit for 5-10 minutes until foamy.
Make the dough: In a large bowl, combine flour, sugar, and salt. Add the yeast mixture, eggs, melted butter, and lemon zest (if using).
Knead: Knead the dough for about 8-10 minutes until smooth and elastic. If the dough is too sticky, add a little more flour.
First rise: Place the dough in a lightly oiled bowl, cover with plastic wrap, and let it rise in a warm place for about 1 hour, or until doubled in size.
Punch down: Gently punch down the dough to release the air.
Shape the Buchteln: On a lightly floured surface, roll out the dough to about ½ inch thickness. Cut out circles using a cookie cutter or a glass.
Fill and shape: Place a spoonful of jam in the center of each circle. Fold the dough over to form a half-moon shape and pinch the edges together to seal.
Second rise: Place the shaped Buchteln on a baking sheet lined with parchment paper, cover with a clean kitchen towel, and let them rise for another 30 minutes.