Pre heat oven 300 Remove all unpopped kernals from popped corn. Place popcorn in greased 17x12x2-inch baking pan. Keep popcorn warm in a 300 oven while making carmel mixture. Butter the sides of a heavy 1 1/2 quart saucepan.in Saucepan combine brown sugar, margarine or butter, and corn syrup. Cook and stir over medium heat to bioling. Clip candy thermometer to side of pan. Cook and stir medium heat to 255 hard-ball stage(about 4 min.) Remove saucepan from heat. Stir in baking soda and vanilla; pour over popcorn. Stir gently to coat. Bake in a 300 oven for 15 minutes; stir. Bake 5 minutes more. Transfer popcorn mixture to large pieces of foil; cool completly. Break into clusters. Store tightly covered. Makes about 9 cups. For an extra bonis you may want to add your favorite kind of peanut.