Preheat Oven to 250
Pop the corn...set aside into Large bowls
Place Sugar, Karo syrup and Salt in a medium saucepan (fairly deep, 6in. height, as for use for spaghetti sauce) and heat to boiling, constantly stirring.
Boil for 5 minutes. NO LONGER!
Lower heat (med-medhigh) but allow mixture to continue to semi-boil(what we want to do here is NOT burn the sugar but keep it bubbling!)
Quickly add (in order) vanilla,nuts(optional), then gently fold and REMOVE from heat, TURN burner on LOW.
Quickly add Baking soda, fold gently ensuring full mix (mixture will puff up 2x-3x larger than what was in the pot)
Immediately pour 1/3 of the mixture over 1/3 of the popcorn in a LARGE bowl, return the remaining 2/3's mixture saucepan to the LOW burner, stir coated-popcorn contantly to coat and cover as much popcorn as you can.
Turn out on a lightly sprayed cookie sheet, repeat until all mixture is on all popcorn.
Yield should be 2 large cookiesheets piled about 3-4inches high
Place in oven at 250 for 30minutes, remove, flip all popcorn over with a spatula, Return to oven for 20 minutes.
Remove popcorn from oven, allow to cool for 2 minutes and break apart.
Call the dentist!