In a large sauce pot melt the butter. Add the onions and the garlic. Sweat the onions and garlic for 3-5 minutes. Add the bratwurst, and all of the beer.
Bring the beer mixture to a boil; reduce and simmer for 15 minutes. Turn off the heat and let the brats cool in the beer mixture.
Heat butter in a sauté pan over low heat. Roll the brats in seasoned flour and brown the sausages on all sides. Serve with sauerkraut.