Preheat grill to high heat. Bring Guinness® Blonde to a simmer with sliced onions, salt and pepper. Add in fresh brats and simmer for 10-15 minutes, turning once, or until cooked through. Reserve 1 cup of beer base and set aside onions.
Char sausages on grill to add color and texture, 5-6 minutes. Next, char each quarter of beer braised onions until deep color forms. Slice off stem and and chop. Toss onions with cherry tomatoes, apple cider vinegar and season to taste.
Place sausage in pretzel roll, then top with creamy spicy stout mustard and charred onion and tomato relish.
Creamy Spicy Stout Mustard
Mix beer cooking liquid, pickled jalapenos, stone ground mustard and mayonnaise all together in a bowl. Adjust thickness with more braising liquid if necessary.