Cover bottom of pan with a thin coat of oil. Once oil is sizzling, add popcorn kernels to fill bottom of pan. Pour popped kernels in large bowl, remove any unpopped kernels.
In large sauce pan, add brown sugar, butter, corn syrup, salt and vanilla. Mix well. Bring to a boil.
Boil for five minutes, stirring constantly.
Remove from heat and add baking soda, stirring until dissolved. Pour syrup over popcorn and mix well. (Optional add-ins; almonds, peanuts, cashews, etc.)
Spread popcorn on large jelly roll pans. You will need a pan with an edge, for stirring up as it bakes.
Add pans to preheated 250 degree oven. Stir every 15 minutes for one hour.
Spread on wax paper or paper bags to cool.
Great for parties! Store in airtight container.