1 Onion (sliced thinly and evenly) 2 tablespoons Olive Oil Beer (just a splash)
In a large skillet over low heat, add the olive oil, and the onions. season with salt, and caramelize. Maintain an even layer, so that onions uniformly cook, stirring occasionally, for 30 to 45 minutes. When carmelized, add a splash of beer.
Form the bratwurst into four patties. Form the ground beef into four patties. Season on both sides with salt and pepper and arrange on grill, being mindful not to crowd the surface, and cook to desired done-ness, about 5 minutes per side. After flipping the ground beef patties, add the cheese to the cooked side of the patty and allow to melt while other side cooks through.
Toast pretzel rolls and assemble sandwiches, sandwiching the gruyere cheese between the bratwurst and ground beef patties, and topping with caramelized onions. Garnish with shasha sauce and ballpark mustard.