In a 5qt. Dutch oven, add onions, green and red bell peppers, Dijon mustard, garlic, butter, and chicken stock. Place on a preheated grill (350 to 400 degrees) and bring to a simmer. Then poke holes on both sides of each brat with a toothpick and place in the Dutch oven. Cover and let simmer for about 5 minutes. Pour in the beer and wine and continue to simmer for 15 minutes.
Remove brats from the Dutch oven with tongs and place on the grill. Cook each side 3 to 5 minutes, or until dark golden brown. Then place them back in the Dutch oven and let simmer for about 5 minutes.
To serve, place each brat into a bun and top with the cooked onions and peppers, and your choice of ketchup, mustard, sauerkraut, pickle relish, and shredded cheese.