The night before, place meat grinder in the freezer. It is important when grinding your own meat that everything be kept as cold as possible so that the fat in the meat doesn't melt. If the fat melts, the meat and fat won't emulsify and you will end up with dry, crumbly burgers.
Dice chuck roast and short rib meat into 1-inch cubes. Combine with bone marrow in a shallow tray and freeze until frozen, but not stiff; about 1 hour. Remove from freeze and season with 5th dimension powder. Grind the meats using the coarse grinding plate. Refrigerate meat again before shaping.
Alternatively, if you don't want to grind our own meat, buy pre-ground chuck and thoroughly combine with 5th dimension powder.
Form into four 6-ounce patties, 1/2 inch thick and season with salt and pepper. Grill until of desired doneness. If grilling over charcoal, set up a two-zone fire, with coals on one side of the grill. These burgers are very juicy and will cause significant flare ups if grilled directly over coals. Alternatively, use an indoor grill set to medium-high heat, about 375 degrees.
Remove to plate and top each patty with a slice of cheese. Tent the plate with foil and allow burgers to rest 3-5 minutes.
Lightly toast hamburger buns and spread with Best Ever Mayo. Top bottom bun with lettuce, then tomato, burger patty and finish with caramelized onions. Makes 4 burgers.