Preheat your oven to 191 °C (190 °C). Lightly grease a 9x13 inch baking dish.

In a large skillet over medium heat, melt the butter or add oil. Add the sliced onions and sauté until softened and lightly golden, about 8-10 minutes. Stir in the sliced apples and cook for another 3-5 minutes until slightly tender.

Add the drained sauerkraut, sliced smoked sausage, brown sugar, Dijon mustard, caraway seeds, and black pepper to the skillet. Stir everything together until well combined.

Transfer the mixture to the prepared baking dish, spreading it evenly.

Cover the dish tightly with foil. Bake for 45 minutes.

Remove the foil and continue baking for another 15-20 minutes, or until the top is slightly browned and the flavors have melded beautifully. The apples should be tender and the sausage heated through.

Let the bake rest for 5-10 minutes before serving.