Preheat oven 250°F. Spray 2 cookie sheets with pam (for easy cleaning use parchment paper on cookie sheets and spray with pam)

In a medium sauce pan, melt butter,sugar, and karo syrup over medium heat. Boil 5 minutes. Remove from heat and add baking soda. Pour over corn in large bowl (may need to do this in 2 batches)

Pour caramel corn mixture on cookie sheets. Bake at 250°F for 1 hour. Immediately spread caramel corn on sheets of wax paper on counter, making sure to spread the pieces apart, cool completely.