Combine 6 cups water, the beer, onion, garlic, ginger, caraway seeds, bay leaves and cloves in a large pot over medium-high heat; bring to a gentle simmer and cook 10 minutes. Add the bratwursts, return to a simmer and cook until almost done (the meat should still be slightly pink in the center), about 15 minutes. Remove from the heat and let the bratwursts cool completely in the cooking liquid, about 1 hour.
Preheat a grill to medium high. Transfer 2 cups of the cooking liquid to a small saucepan over medium heat. Add the butter and bring to a boil; cook until the butter melts, about 1 minute.
Grill the bratwursts, occasionally turning and basting with the butter mixture, until marked and cooked through, 10 to 12 minutes. Serve on rolls with mustard and other toppings.
Cook 2 chopped red onions in a skillet with 2 tablespoons olive oil over medium-high heat, stirring, until golden, about 8 minutes. Add 1/2 teaspoon caraway seeds; cook, stirring, 30 seconds. Add 1/4 cup red wine vinegar, 1 tablespoon brown sugar and 1/2 teaspoon kosher salt; cook, stirring until the onions are glazed, 1 minute. Let cool completely.
Bell Pepper Relish
Pulse 1 each chopped yellow bell pepper and orange bell pepper, 4 each chopped radishes and scallions, 1 chopped celery stalk and 1 garlic clove in a food processor until finely chopped. Whisk 2 tablespoons each cider vinegar and chopped parsley, 1 tablespoon olive oil, 2 teaspoons brown sugar, 1/2 teaspoon each celery salt and kosher salt, and pepper to taste in a large bowl. Add the vegetable mixture; toss to coat.
Smoky Beer Cheese
Combine 1/4 pound each shredded sharp cheddar and smoked gouda, 1 minced garlic clove, 1/2 cup lager beer, 2 teaspoons hot sauce, 1/2 teaspoon kosher salt, and pepper to taste in a food processor; pulse until smooth.
These toppings also taste great on burgers or hot dogs.