Heat the milk and sugar lukewarm in the microwave. Crumble in the yeast and use a fork to dissolve. Put the flour, a little salt and the butter in a bowl. Add the yeast milk and knead everything into a smooth dough. Cover and let rise in a warm place for 45 minutes.
Peel the onion and cut into rings or slice finely with a food processor. Heat the oil in a roasting pan. Fry the ham cubes in it and add the onion and sauté everything for about 15 minutes until translucent. Season everything with pepper and salt, let cool.
Knead the dough again, then place it in a greased quiche dish and roll out, pulling the edge up about 1 cm. Cover and let rise again for about 15 minutes.
Mix the sour cream, eggs, 1 teaspoon salt and the caraway seeds together. Pour the onion mixture on the dough and pour the cream sauce over it.