Tapenade-Filled Burgers

Divide beef into 6 portions. Divide 1 portion in half, then flatten 1 half into a 4-inch patty and form a 1/4-inch rim around patty.

Spread 1 1/2 tablespoons of tapenade onto patty within rim. Flatten remaining half into a 4-inch patty, then lay on top of tapenade-covered half and pinch edges together to seal. Pat side to form a straight-sided edge and transfer to a large tray. Make 5 more tapenade patties in same manner and transfer to tray, then refrigerate patties, covered, until ready to grill.

Prepare grill for cooking over direct heat with medium-hot charcoal (moderately high heat for gas); see "Grilling Procedure."

Sprinkle patties on both sides with salt and pepper. Lightly oil grill rack, then grill patties (covered only if using a gas grill), turning over once, 3 minutes total for medium-rare. (Burgers will continue to cook slightly after being removed from grill.)

Spread mayonnaise and mustard on buns, then assemble burgers with onion, pickles, and romaine.

· Patties can be assembled up to 8 hours ahead and chilled, covered.· If you can't grill outdoors, patties can be cooked on a lightly oiled well-seasoned large (2-burner) ridged grill pan over moderately high heat, turning over once, 4 minutes total for medium-rare.