For a good introduction to Southern, I'd take your friend to Mary Mac's Tea Room, on Ponce de Leon, just northeast of downtown. It's the traditional Southern-style tea room, with pretty good fried chicken, cornbread, collard greens (good pot likker, too!) This isn't quite down-&-dirty soul food, more Southern grandma cuisine. Good biscuits, sweet tea, macaroni casserole, and the like. Supposedly this is where a lot of high-powered people eat lunch (Coke execs, etc.). Maybe you'll get lucky and be greeted by the 85-year-old identically dressed twins.