Ensure you have a large skillet with a lid. Heat the duck fat in the skillet over high heat. When the duck fat shimmers, add the diced potato. Cook for 4-5 minutes, turning frequently until the potato turns golden brown.
Add the sliced raw sausage. Cook until browned, about 2-3 minutes. Please note that the bratwurst will still be undercooked, so do not sample it yet!
Add 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 the sauerkraut and cooked bacon.
Cook the sauerkraut mixture uncovered for 1 to 2 minutes to allow some moisture to cook off. Then cover, reduce the heat to medium-low, and cook for 15 minutes, stirring 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!