Preparation Fashion beef into 6 patties no more than 1/4 inch thick and season each patty with salt. Spread bottom half of each bun with 1/2 tablespoon softened butter. On a griddle or in a large heavy skillet fry onions in additional 3 tablespoons butter over moderately high heat, stirring, until barely softened, and push to side of griddle or skillet. Fry burgers, flipping once, about 2 minutes on each side for well-done. Transfer burgers to buttered bun bottoms while still hot (to melt butter) and top with onion, tomato, and lettuce. Spread condiments on bun tops. Serve burgers with plenty of napkins.
Preparation Fashion beef into 6 patties no more than 1/4 inch thick and season each patty with salt. Spread bottom half of each bun with 1/2 tablespoon softened butter. On a griddle or in a large heavy skillet fry onions in additional 3 tablespoons butter over moderately high heat, stirring, until barely softened, and push to side of griddle or skillet. Fry burgers, flipping once, about 2 minutes on each side for well-done. Transfer burgers to buttered bun bottoms while still hot (to melt butter) and top with onion, tomato, and lettuce. Spread condiments on bun tops. Serve burgers with plenty of napkins.