Ketchup Mustard Mayonnaise COMBINE OIL AND ONION in a small skillet over medium heat and cook, stirring, about 4 minutes, or until onions soften. Add garlic, pepper, nutmeg and coriander and continue to cook another minute. Scrape the onion mixture into a mixing bowl, add the beef and mix well. Form 4 patties, place on a plate, cover and refrigerate for 20 minutes. Place a large, heavy skillet on the stove over high heat. When it is nearly smoking, add the hamburger patties. Cook 2 minutes. Turn the patties and cook on the other side until desired doneness, about 1 minute for very rare, 4 minutes for medium-well. Arrange burgers on hamburger buns and garnish each with a slice of onion and tomato. Offer ketchup, mustard and mayonnaise.