In the meantime, fry your onions and bacon. In a separate frying pan, fry your sausages.
When the sauerkraut and potatoes are done, mash them together with some butter and milk. Add the onions and bacon and stir until it is a nice smooth consistency.
Put this mixture in a casserole dish or other serving dish. Then you have an option, to either slice the sausages on top of the casserole or serve them separately.