In a small bowl, combine the yeast and sugar with a bit of the lukewarm milk, letting it sit until frothy, about 5 minutes.

Mix the rest of the milk with the flour, butter, salt, and knead for 5 minutes. Cover the dough and let it rise in a warm place until it has doubled in size, about 1 to 1 ½ hours. Meanwhile, grease your baking dish with butter.

Peel and slice the onions into rings. In a large skillet over medium heat, cook the onions in butter until they become soft and translucent, without browning, which should take about 10 minutes or more. Stir in the flour and let the mixture cool. Season generously with salt.

Beat the eggs and cream together. If desired, stir in the caraway seeds or sprinkle them on top later.

Press the dough evenly into the baking dish, extending it about 1 inch up the sides. (Note: A 9.5-inch pan works well, but a larger pan will result in a thinner pie.)

Spread the onion mixture over the dough, then pour the egg-cream mixture on top. Scatter the diced bacon over the surface and sprinkle with caraway seeds if using.

Bake in the middle of the oven at 390° F for 35 to 45 minutes. The pie is done when the center is set and the crust is golden brown.

Let the pie cool for at least 10 minutes before serving. Enjoy with a glass of Federweißer or Riesling and a fresh green salad. Guten Appetit!