Form ground beef into two flat patties and season with salt and black pepper.
Melt butter in a skillet, sauté sliced onions until soft; remove.
Sear beef patties on high flame for 4 minutes per side.
Top patties with barbecue glaze (mix tomato sauce and vinegar) and cheddar slices to melt.
Toast burger buns and assemble with patties and cooked onions.