Be sure you are using a large skillet that has a lid. Heat the duck fat in the skillet over high heat. When the duck fat shimmers, add in the potato. Cook for 4-5 minutes, turning frequently as the potato browns.
Add in the sliced bratwurst. Cook until browned, about 2-3 minutes. Please note that the bratwurst will not be cooked through, so no sampling yet!
Introduce the onions and shallots to the bratwurst and potatoes. Give them a pinch of salt to release their water. Stir frequently to prevent burning. Cook until lightly browned.
Reduce the heat to medium and add in the garlic. Stir for 1 to 2 minutes and then add in the sauerkraut and cooked bacon.
Cook uncovered for 1 to 2 minutes to allow some of the moisture to cook off. Then cover, reduce the heat to medium low and allow to cook for 15 minutes. Stir every 5 minutes or so.
Check if the potatoes are cooked through. When they are cooked through, you're ready to eat.
Serve in bowls. Top with sour cream and a sprinkle of paprika. Enjoy and happy eating!