Mix sugar, syrup, and butter in heavy saucepan. Bring to boil and cook 5 min. Remove from heat, add baking soda, cream of tartar, and salt. Pour over popped corn immediately.
Spread mixture on a baking sheet and bake at 200F for 1 hour.
Recipe by Opsreys Journeys at https://www.ospreysjourneys.com/?p=2896