Stir the sauce ingredients together. Chill for at least 1 hour.
Season the beef, then gently form six large, flattish patties. Grill for 3 minutes each side for rare, or longer if you prefer, on a medium-high heat (don’t push down on the burgers or the juices will escape). Grill further to melt a slice of cheese on top.
To serve, put a burger on each halved bun. Top with bacon, onion, tomato, lettuce, a tablespoon of Blt sauce and a bun half.