Customers arrive at Ridgewood Barbecue in Bluff City, Tennessee. Photo ©Sherry Jacobson/Texas BBQ Posse) In Bullock’s Hollow, there are culinary secrets galore. Amid the Appalachian Mountains of Eastern Tennessee, you’ll find Ridgewood Barbecue. It opened in 1948 and still attracts a full house of customers, even on a recent Friday not long before New Year’s. That’s when Sherry and I visited with friends Phillip and Trish Townsend, who live an hour or so away in North Carolina. The secrets? Start with the recipe for the tomato-based sweet and sour barbecue sauce, which goes on much of the food the place…