Preheat oven to 350°F. In the pieshell, place sugar, flour, and salt. Mix with your fingers. Pour the evaporated milk over the flour and sugar BUT DO NOT STIR. Drop butter in small amounts on top around the pie. Sprinkle cinnamon over the top. Bake for 50 minutes, or until filling bubbles up in the center. The filling will not completely set but that's how it's suppose to be. Pie is best eaten at room temperature. This is so good!