Boil ½ clear corn syrup, 1 c butter, 1 tsp salt, 1 tsp butter flavoring, and 2 c brown sugar in a saucepan until it reaches 245 °F. Add 1 tsp baking soda and stir.
Pour syrup mixture over 4 qt popped corn.
Bake in dish for 1 hour, stirring every 15 minutes.
Remove from oven and stir until cool, place in plastic bags. May be frozen.