Satisfying and super easy at-home brewery-worthy grilled bratwurst subs topped with ale-caramelized onions, sauerkraut, and grainy mustard.
1. Melt butter in a large skillet. Add onion, salt, brown sugar, and apple cider vinegar. Sauté over medium heat for 5-7 minutes until softened. Add beer and simmer over low heat, stirring often, for 20 minutes until onions are caramelized.
2. Meanwhile, grill bratwurst until charred and warm and toast sub rolls.
3. Serve on sub rolls, topped with ale onions, sauerkraut, and grainy mustard.