In a bowl combine the ground beef, cream, Worcestershire sauce, salt, and pepper.
Divide the meat mixture into three even patties (1/3 lb each). Roll into balls and then flatten to desired thickness. Make sure to form the patties so they are larger than your buns. The 80/20 mixture includes more fat and will shrink slightly during the cooking.
Grill the burgers on medium high to high heat (I set my grill at 400-425 degrees F) 8 minutes per side or until the burgers are cooked throughout and reach an internal temp of 160 degrees. Top with a piece of cheese to melt.
Place the onion slices in the buttermilk and let soak for a couple of hours or overnight.
In a bowl, combine the flour and salt.
Heat the oil to about 375 degrees in a heavy bottom pan or fryer. Working in batches take the onions from the buttermilk and toss into the flour. Shake off the excess coating and place into the heated oil. Fry 3-5 minutes or until the stings are golden brown. Remove to a paper towel lined plate. Repeat through the rest of the onions.
Combine the mayonnaise and ketchup. Let sit in fridge until time to assemble burgers.
Toast the buns in a pan with a little butter. Put a layer of the sauce on the bottom bun, top with the burger patty and cheese. Add a slice of bacon (or two) and a handful of the onion strings. Smear a little more sauce on the top bun.