Preheat grill. Bring beer and water to a simmer in a large saucepan over medium-low heat. Add Kitchen Accomplice Beef Broth Concentrate or Beef Bone Broth Concentrate and whisk until it dissolves. Add onions. Pierce each bratwurst in several places with a fork and add to simmering liquid. Bring liquid back to a simmer and cook 10-15 minutes, until brats are nearly cooked through.
Transfer the brats to grill and cook another 8-10 minutes, turning halfway through, until browned on both sides.
Place each beer-braised brat in a roll and spoon on mustard. Serve with your choice of pickles, chopped onion, ketchup and sauerkraut.
Note: In Sheboygan, Wisconsin, said to be the Brat Capitol of the World, Bavarian mustard, pickle, and chopped onion are the typical toppings for brats. The addition of ketchup is considered a crime by some, but acceptable by others. Sauerkraut is generally frowned upon, but we like it with our brats, and you might, too!