In a deep skillet or Dutch oven, add the raw bratwurst, 1 sliced onion, the beer (enough to cover the sausage), and ½ of a stick of butter cut into cubes.
Bring the water to a slow boil, turn down the heat to medium-low, and simmer the brats for 10 minutes. They should be mostly cooked (aka par-boiled) and will finish cooking when you grill or pan cook them.
Remove the bratwurst from the liquid and either grill them on a preheated grill for 10-14 minutes until browned. Or you can pan fry them in a skillet with a little oil or butter for 3 minutes on each side. Add the onions back to the pan also if you're pan-frying them to serve with the sausages.
