Brown the Brats Heat butter or oil in a large skillet over medium heat. Add the bratwursts and cook for 5–7 minutes, turning occasionally until browned on all sides. Remove and set aside.
Cook the Onions In the same pan, add sliced onions and bell peppers. Cook for 6–8 minutes until soft and lightly caramelized.
Add Beer & Simmer Return the brats to the skillet. Pour in the beer and optional broth. Add brown sugar if using. Bring to a gentle simmer and cook for 10–15 minutes until the brats are fully cooked.
Finish & Reduce Sauce Allow the liquid to reduce slightly to create a flavorful sauce. Taste and adjust seasoning with salt and pepper.
Serve Place brats in buns, top with onions, mustard, and sauerkraut. Spoon extra beer sauce over the top for added flavor.