SARA LEE is no role model for Alan Rupp. She sold out.

Sure, Alan Rupp. She sold out.

Sure, Alan Rupp hopes to expand his Derby Pie business from 50,000 to 100,000 pies a year and to ship frozen pies coast-to-coast, but sell out?

Hardly. In fact, he has a lawyer who spends two to four hours a week doing nothing but defending the good--and exclusive--name of Derby Pie. Invented by Rupp's grandmother, Leaudra Kern, and produced by her for a couple of decades until Rupp took over in 1973, this Louisville, Ky., specialty has been imitated by restaurants and cookbooks all over the country.

But the only legal Derby Pies made by Kern's Kitchen Inc., the official title of the Rupps' pie company, which may sound like a big outfit but consists of curly-haired, bearded Alan and his red-haired wife Sheila, both age 27, his brother and sister-in-law and the Rupps' home kitchen. It's about as modest as a home kitchen can be without being considered a galley.

After Saturday's Kentucky Derby, their busiest time, the Rupps are moving to a new kitchen. And in the past year they bought a Vulcan oven, so they can bake 23 pies at a time rather than only six as they used to do in their two home ovens. This year they also rented freezer storage in a friend's garage once they started, last February, gearing up for Kentucky Derby sales. But the filling is still mixed for only 10 pies at a time in their two KitchenAid mixers and the ingredients are still weighed on a home-size scale.

"The Original Derby Pie" is truly original. It is a shallow pie with a bottom layer of chocolate chips and over it a starchy, very sweet filling that separates when it bakes into three layers: one spongy, one of nuts and then a very thin and flaky top. Rupp insists it should be served warm, for a better blend between the nuts and chocolate, perhaps with whipped cream. Sheila complains that not only do some restaurants serve it cold, "Some put 'em in the microwave and fry 'em," so that the nuts are sizzling and popping.

What's worse, though, is when other restaurants serve a pie the Rupps haven't made and call it Derby Pie, or tell a customer (who may be Rupp, for he is constantly checking), "It's like Derby Pie." Then Rupp stands up and defends his pie--not quietly--and his lawyer, Bob Donald, gets on the case. Donald sends an average of a letter a week to restaurants, authors and newspapers to protect the pie's trademark. "They're allowed to have one free bite," said Donald; if they repeat the infringement, he's ready to sue. Lately he's even been sending letters to cookbook publishers and the National Federation of Women's Clubs, to try to forestall trademark violations.

By now the pie's friends around the country report any infringements they spot. And Louisville cookbooks and restaurants have learned to call their imitations "Chocolate Chip Pie" (Entertaining the Louisville Way by the Queens Daughters Inc.), "Favorite Louisville Pie" (The Farmington Cookbook), "Run for the Roses Pie" (The Louisville Times) and "Louisville's Finest Pie" (Hyatt Regency Hotel). One Louisville cookbook has "Derby Pie" blackened out on the page and replaced by "Queen's Pie," but the index still lists it as Derby Pie. Even the Giant supermarkets in Louisville sell a pie vaguely reminiscent of Rupp's.

The only thing about Rupp's pie that is not a mystery is how it got its name. "I asked Grandma that on the last lawsuit," said Rupp. She had dreamed up the pie while her son George, Rupp's uncle, was managing the Melrose Inn in Prospect, a suburb of Louisville, and the name was simply pulled out of a hat.

The recipe, however, has remained a secret that only six people know: Kern, her daughter and the four grandchildren who share in the pie-making. Alan's father doesn't know. Neither his 4-year-old niece nor his lawyer is allowed in the kitchen during the pie making. His other siblings aren't in on the secret. Sheila was told the recipe on her wedding day, a week before she started making Derby Pie. "I can't cook, either," she admitted. "It's the only thing I've learned to cook."

Details do, however, leak out. Bob Donald figures that there are eggs in the pie because he sees the cartons. He learned there's no bourbon in it during the big lawsuit against a distillery that tried to use the pie's name on a bourbon-spiked version. The Rupps say that they buy their chocolate chips directly from Nestle' and their walnuts from Diamond, so those are certainly ingredients. Their kitchen is stacked with bags of sugar and flour; their freezer is filled with pie shells, which--since 1978--they have been buying rather than making themselves. And Sheila was so bold recently as to tell a reporter two heretofore unrevealed secrets: The chocolate chips are scattered on the bottom of the shell before the filling, and the filling is poured from a pitcher gently in a circular motion so as to leave the chips undisturbed.

Sheila hand-picks a hundred pounds of walnuts every evening or two, and grinds them in a home-size KitchenAid. By now she can bake 200 pies a day, and can still manage to eat a piece a day, justifying it by consuming only pies that don't look just right. "Last week," she admitted, "I ate half a pie. It's the only time I get a glass of milk." She doesn't even notice the Derby Pie smell any more, but guests claim that they can smell their way up the Rupps' driveway, even if it is not a baking day.

Derby Day, of course, is their big day. The pie is sold at both racetracks, Churchill Downs and Louisville Downs. And this time of year there is always a revival of the joke that the pies are made out of losers from the tracks. Some restaurants expect to sell a hundred pies in this one week; the pies are sold in motels, clubs, retail stores, even state parks, and they are sold as far away as Cincinnati. For awhile the Rupps fiddled around with selling Derby Pies in New York, but gave up because shipping doubled the price. But they talk about going national eventually, and such expansion will put a new kind of pressure on the Rupps' secret--ingredient labeling. In the meantime, people aren't going to get one morsel of the recipe from them.

What are people outside Louisville supposed to do? Rupp doesn't even need to pause to consider the answer: "Wait till I get there."

The following recipes are not Derby Pies. We wouldn't want to increase Bob Donald's workload. But they are examples of recipes that have tried to be Derby Pies, which fall into two general categories. The first looks and tastes pretty close, though some versions add less flour, some use black walnuts or pecans. The second, using corn syrup, is more like a traditional pecan pie, but with chocolate chips and a Louisville touch, bourbon. Of the various Louisville pies tested, these were the two most universally preferred.

NOT DERBY PIE 1 unbaked pie shell 1 cup chocolate chips 2 eggs, slightly beaten 1 cup sugar 1/2 cup flour 1/2 cup (1 stick) butter, melted and cooled 1 cup walnuts, coarsely ground 1 teaspoon vanilla Whipped cream for garnish (optional)

Sprinkle bottom of the pie shell evenly with chocolate chips. Combine eggs with sugar and flour. Gradually mix in butter, then nuts and vanilla. Carefully pour mixture over the chocolate chips, in a circular motion so that it does not disturb the chips. Bake at 325 degrees for 1 hour. Serve slightly warmed, with whipped cream if desired.

UPS-AND-DOWNS PIE 1 unbaked pie shell 1/2 cup chocolate chips 1 cup walnuts or pecans 4 eggs 1 cup sugar 1 cup white corn syrup 1 stick butter, melted and cooled 1 tablespoon bourbon

Spread chocolate chips and nuts over bottom of pie shell. Beat eggs. Add sugar and corn syrup, then gradually add butter and bourbon. Pour carefully into pie shell. Bake at 350 degrees for 45 minutes, or until set.