In 2½ quart saucepan, combine brown sugar, corn syrup, butter, cream of tartar, and salt. Bring to boil, stirring over medium high heat.

Stirring constantly, boil rapidly until mixture reaches 260° on candy thermometer.

Remove from heat. Stir in baking soda quickly but thoroughly. It will bubble!

Pour at once over popped corn in large baking pan. Stir gently until all kernels are coated. If you are doubling it you will need someone to help you do this FAST. Bake at 200° for 1 hour, stirring 2 or 3 times during baking.

Turn out at once on wax paper. Spread apart and allow to cool completely. Break into small clusters. Store in tightly-covered containers.