Preheat oven to 250 degrees.
In a large pan, heat peanut oil on high heat (about 20 seconds).
Add popcorn, cover pan and agitate. Remove from heat once kernels slow their popping and pour popped corn into 20x13x3 aluminum roasting pan. Remove any uncooked kernels.
Melt butter in a large saucepan, then stir in brown sugar, corn syrup and salt. Bring to boil, stirring constantly.
Boil without stirring for 5 minutes. Should be a slow boil as not to burn (use medium heat).
Remove from heat and stir in baking soda and vanilla.
Gradually pour over popcorn and mix well.
Bake in oven for one hour, stirring every 15 minutes.
Remove from oven and, as caramel corn cools, completely break apart and store in tightly covered container.