3/4 cup yellow onion, finely minced
  2 tablespoons butter

  1 1/2 lbs lean ground beef
  2 tablespoons butter, softened
  1 1/2 teaspoons salt
  1/8 teaspoon pepper
  1/8 teaspoon thyme
  1 egg
  1/2 cup flour, spread on a plate
  1 tablespoon butter
  1 tablespoon oil

  1/2 cup beef stock, beef bouillon, dry white wine, dry white vermouth, red wine, or 1/4 cup water
  2-3 tablespoons butter, softened
  2 tablespoons green herbs, minced (such as parsley, chives, tarragon, or chervil)

  In a large skillet over medium heat, add the 2 tablespoons butter and onions and cook slowly until soft but not brown, about 10 minutes. Transfer to a mixing bowl and set aside.
  To the mixing bowl, add the beef, 2 tablespoons softened butter, salt, pepper, thyme, and egg. Beat vigorously with a wooden spoon until well mixed.
  Form mixture into patties 3/4 inch thick and cover and chill until ready to use.
  When ready to cook, lightly roll patties in flour spread on a plate, shaking off excess.
  In a skillet over medium-high heat, heat the 1 tablespoon butter and oil. When it begins to foam and subside, sauté the patties to desired temperature, about 2-3 minutes or more per side depending on doneness.
  Transfer patties to a plate and keep warm while you work on the sauce:
  Drain fat from skillet. Add liquid (stock, wine, etc) and let boil, scraping up bits from bottom of pan as it reduces. Cook down to almost a syrup consistency, then turn off heat, and add butter by 1/2 tablespoons. Swirl pan to melt butter, then stir in herbs.
  Spoon sauce over hamburger patties and serve. Enjoy!