Place water in a stockpot on high and bring to a boil.
Meanwhile, heat the oil in a sauté pan. Add the onions and season with salt and pepper. Allow the onions to sweat for 5 minutes.
Move the onions to the outer edge of the pan, and place the bison brats in the center. Cook for 3 minutes on each side.
Slowly pour the beer into the pan, and simmer on medium until the liquid has evaporated.
Meanwhile, gently place the cabbage leaves in the boiling water and boil for 5 minutes or until tender. Remove from the pan and place on paper towels to dry.
Place 2 to 3 cabbage leaves of cabbage, depending on their size, on a plate. Place 1 brat and the desired amount of sauerkraut on the leaves then fold their ends in and roll up, creating a nice tight wrap. Serve and enjoy!