Gourmet burger topped with sautéed mushrooms and melted Swiss cheese. Restaurant quality at home.

Sauté mushrooms and onions in butter until golden, about 8 minutes.
Add wine if using and cook until evaporated.
Form beef into 6 patties and season with salt and pepper.
Grill or cook patties 4-5 minutes per side.
Top with Swiss cheese in last minute of cooking.
Mix mayonnaise and Dijon mustard for sauce.
Assemble burgers with sauce and mushroom mixture.