INGREDIENTS (1 1/4-inch-thick) New York strip steaks (each about 6 ounces) 8 tablespoons (1 stick) chilled unsalted butter, divided 1 large shallot, minced 1/2 cup balsamic vinegar 2 large fresh rosemary sprigs 2 pounds mixed sweet onions, large shallots, baby leeks, and green onions 2 tablespoons olive oil 2 tablespoons orange juice DIRECTIONS Melt 6 tablespoons butter in heavy small saucepan over medium heat. Add minced shallot and cook until translucent, about 2 minutes. Add vinegar and rosemary and simmer until syrupy and reduced to 1/2 cup, about 6 minutes. Remove from heat (balsamic sauce will separate as it stands). Prepare barbecue (medium-high heat). Peel sweet onions, then cut into 1/2-inch-thick rounds. Skewer horizontally with toothpicks to keep intact. Peel shallots; cut in half lengthwise. Trim root ends and tops of leeks. Cut in half lengthwise; rinse to remove any dirt. Trim root ends of green onions. Place sweet onions, shallots, leeks...