'Tis a monstrous thing, this double-decker piled high and sliced in substantial halves, not those traditional quarters. That single diagonal cut, though, is as far as Express Deli, the all-purpose lunch counter-grocery on the ground floor of Houston House apartments, strays toward the experimental. Sure, you can choose your cheese and take it on toasted white or wheat, but the time-honored recipe has little room for variation from the standard stacks of turkey, ham, lettuce, tomato and bacon, with mayo, thanks. And there, in that structural stability, lies its continuing value as comfort food. Few clubs are as comfortable as Express Deli's -- might have something to do with counter guys who remember your name after you've ordered just once. Long may it stand.