Melt 1 tbsp butter in a medium skillet, add onions, season with salt and saute on medium til translucent. About 3-5 minutes.
Put the bratwurst in a medium-large pan on medium high and cook covered til done. 3-5 minutes per side
When the onions are translucent, add the remaining ingredients. Bring to a boil, then simmer until all the beer is gone. About 8-10 minutes.
In a large mixing bowl combine the cheeses with the flour. Toss to coat thoroughly.
In a medium sauce pot saute garlic, then add 1 cup beer and bring to a boil. Then cut the heat.
While constantly stirring, slowly sprinkle in cheese. Wait for cheese to melt before adding more. If you're not patient your sauce will come out clumpy.
Halve and butter the kaiser rolls. When the sausage are done, set them aside, drain the pan and toast the kaiser buns in the pan.
Bisect the sausages length and width wise. Place 3-4 pieces on the bottom piece of each Kaiser roll, top with cheese sauce and onions. Server with more beer.