I bought my "roast beef classic" ($5.95) off the rack. Watercress, beefsteak tomatoes, sliced onion, and horseradish all sounded good; today, though, I just didn't have time to wait for a sandwich made from scratch (which doesn't seem to be common here in any event). "Beefsteak" shouldn't mean that the tomatoes are sliced thicker than the layer of roast beef.
Fluffy's Cafe & Bakery
855 Seventh Ave. (54th-55th Sts.)