If you’re going to be grilling these little beauties outside, get the fire started now so it’s ready when the Brats are. In a large skillet, melt butter over medium heat. Add sliced onions and salt and pepper. Sauté until onions just start to soften. Add in the Guinness. Add whole sausages to the beer and onion mixture; do not cut up the sausage. Simmer uncovered over low-medium heat for approximately 10-12 minutes. Remove sausages and continue to cook onions over low heat until brats are ready. Grill the whole brats over medium heat for 3-5 minutes on each side, just long enough to form a nice grill mark.