FORTY YEARS AGO, when most Americans thought there was no better place to shop than the supermarket, Lancaster County promoted itself as a center of local foods and traditional dishes. Then, as the rest of the world became more and more interested in these things, Lancaster became less so. Amish families that had been farming for generations were suddenly working in retail stores and factories and their land gradually became subdivisions and shopping centers. Now, just when you thought that the area had been turned into an endless mall, a whole new generation of farmers is bringing back the idea of local food. Produce is organic, livestock is grass-fed, and a growing number of people are creating cheeses that are world-class.