Recipe

Cook Onions

1. Heat oil in large, heavy pot (not nonstick) over medium heat. Add onions. Cook, undisturbed, until onions are wilted and browned on bottom, 20 minutes. Add splash of water. Stir with wooden spoon, deglazing pan.
2. Repeat process 2 more times, or until onions are soft and dark brown, 45 minutes in total. Stir in thyme and vinegar. Season with salt and pepper. Remove from heat and cool. Transfer to airtight container. Refrigerate for up to 1 week.

Make Burgers

1. Place grinding attachment in freezer. Place beef on tray and freeze for 20 minutes. Grind beef using medium plate. Divide into 4 loose, even balls; gently form into patties. Push dimple in center of each patty with thumb.
2. Preheat grill to medium-high. Oil grate. Season patties generously with salt and pepper. Grill until desired doneness, 3 minutes per side for medium rare, 5 minutes per side for medium well. Top patties with cheese slices during last minute of cooking. Transfer to platter.
3. Toast cut sides of buns on grill. Serve burgers with onions, ketchup and lettuce.