In a 4-6 qt cold crockpot, wipe the dish with butter (it will be thick, but that's fine). Add onions, potatoes, garlic chili flakes, paprika, salt and pepper. Next layer the Kielbasa, then the sauerkraut. Finally, pour the chicken stock over it all.
Crockpot settings vary with brands, I cooked this on "high" for 4 hours mainly to cook the potatoes.