In a
large skillet, cook the bacon over moderately high heat, turning
once, until crisp, about 6 minutes. Drain and cut the bacon into
large pieces.

Light
a grill to medium high and fill a large bowl with ice water.
Gently mix the ground chuck with the ground sirloin, salt and
pepper. Form the meat into six 4 inch patties, about 1-1/4 inches
thick. Press an indentation in the center of the burgers with your
thumb. This will prevent them from developing a bulge when
grilling in the center of the burger.

Immediately
transfer the burgers to the grill. Do not flip the burgers until a
good browned crust has formed. Grill over medium-high heat for 9
minutes for medium.

Top
the burgers with the cheese during the last minute of grilling and
let melt. Set the lettuce leaves and tomato slices on the bottom
halves and top with the burgers, onion relish and bacon. Close the
burgers serve immediately.

Serves:
6