1/4cupbeer mustard, or more if needed (you can buy store-bought or make it homemade, but I just mixed a few tablespoons of Dijon mustard with a little bit of beer)
1 1/2poundsground beef
burger seasonings(seasoned salt, pepper, etc.), if preferred
8to 12 thin slices black forest ham
In a medium skillet, melt butter over medium heat. Add the onions and saute until just barely soft, about 8 to 10 minutes. Pour in the beer then stir. Cover and cook for 10 more minutes. Remove the cover and continue to cook until most of the liquid is evaporated, about 5 minutes. Stir in 2 Tablespoons of the beer mustard; set aside.
Meanwhile, shape the ground beef into 4 thick patties, mixing in seasonings to taste. Grill to desired doneness, adding the slices of cheese near the end and allowing to briefly melt. Toast the pretzel buns on the grill, if preferred. Remove buns and burgers from the grill and place on a platter to prepare for assembly.
To assemble the burgers, place a leaf of lettuce on the bottom half of a pretzel bun. Place a burger patty on top of the lettuce, with the cheese facing up. Top with beer-braised onions, beer mustard and 2 to 3 slices of ham. Finish it off with the top half of the pretzel bun. Repeat with the other patties and ingredients. Open your mouth wide, take a big bite and prepare to be amazed with the best burger ever.