Grilled London Broil with Horseradish Cream and Charred Corn

London broil is not a cut but a method: marinate a thick, lean steak, grill it quickly and slice it very thin across the grain. Top round is the usual choice, and the overnight marinade is what keeps it from being tough. Never cook it past medium-rare. Horseradish cream is the classic sharp, cooling partner, and it takes two minutes to stir together. Grill the corn and tomatoes on the same fire while the steak rests, and bring everything out on a cast iron platter.