Preheat oven to 350 F. In the pie shell, place the brown sugar, flour, and salt. Mix with your fingers. Pour the evaporated milk over the flour and sugar, but do not stir or mix this in. Dot with butter, and drift cinnamon liberally over all. Bake for 50 min., or until the filling just bubbles up in the middle. The filling will never completely set, but that's the way it's supposed to be. This pie is better eaten at room temperature. If you refrigerate leftovers, reheat them in the oven before serving. Note: Recipe can be doubled and prepared in a 10 inch pie shell. For that size, bake 1 hour and 20 min. (Yield: 12 servings)