Some trace the origin of the hamburger to the St. Louis World's Fair of 1904. Would we be spoilsports to point out that others date the delicacy all the way back to ancient Rome, and beyond? As edifying as it may be to read accounts of Tartar warriors toting filets off to battle under the saddles of their horses -- aiming to nosh later on the raw, tenderized result (voilà, steak tartare!) -- it all comes down to drawing a line at how you define. Which brings us to the newer and more generic term, burger, about which our trusty Amercian Heritage Dictionary has this to say: "n. Informal. 1. A hamburger. 2. A sandwich similar to a hamburger but with a nonbeef filling: a crab burger." For our $10, no local beefless burger tops the Cajun crab cake sandwich served at Brandt's Cafe in the U. City Loop. The fixings are basic: a modestly seasoned crab burger, heavy on the crab and light on the filler; lettuce, tomato, red onion and a bun. And, to top it off, a generous squiggle of spicy aioli. Now that's tasty!