Terry Allen sings ''Gone to Texas'' as we cross back over the Sabine and head for Beaumont, where Melanie Dishman, a friend of a friend, has promised to make us a traditional crawfish etouffee. Dishman, who has a degree in speech communications from Beaumont's Lamar University and years in the catering business, has worked is now development director for KVLU, her town's public radio station, and lives in a handsome, art-filled town house that could be situated in any good-size city in America. But her family owns a farm in nearby China, where they grow soybeans, blackberries, and rice, and Dishman grew up eating ''great fried chicken, Sunday roast with rice and gravy, and lots of crawfish. Around my house, if you didn't peel crawfish fast enough, you didn't get any. If you had a sore thumb, it meant you'd had a great afternoon.'' Texas Cajuns eat pretty much the same food as their Louisiana counterparts, she tells us, as she starts chopping celery, green peppers, onions, and the tops of some green onions for her etouffee. (''What do you do with the white parts?'' I ask her. ''Oh, I just put them in the refrigerator until they get rubbery, and then throw them away,'' she cheerfully replies.) But a good etouffee, Dishman adds, isn't easy to find. ''When I started ordering it in restaurants,'' she remembers, ''I thought it would be like my mother's. But so many people use tomato products in it, which is just wrong. I can look across a room and tell if an etouffee is one I want to eat.''