In 2 1/2 qt saucepan combine brown sugar, corn syrup, butter, cream of
tartar, and salt. Bring to a boil, stirring, over med high heat.
Stirring constantly, boil rapidly to hard ball stage, 260F (about 5
mins). Remove from heat. Stir in baking soda quickly but thoroughly,
pour at once over popcorn in a lg roasting or baking pan. Stir gently
until all kernels are coated. Bake 200F for 1 hr, stirring 2-3 times
during baking. Turn out at once on wax paper, spread apart and allow
to cool completely. Break apart, store in a tightly covered container.