Melt butter, stir in brown sugar, sorgum, salt. Bring to boil without stirring, 5 minutes. Remove from heat. Stir in soda and vanilla. Gradually pour over popped corn mixing well. Turn into 2 large shallow baking pans. Bake at 250* for 1 hour, stirring every 15 minutes. Remove from oven. Cool completely. Break apart and store in tightly covered container. Makes about 5 quarts carmel corn.