Baked Caramel Corn

This is a recipe I've had for many years.  I think it originally came from a pamphlet of popcorn recipes.  We have enjoyed it over the years, it's quite addictive!  We really enjoy having it around for the holidays and giving it to friends. 

Baked Caramel Corn:
1 cup (2 sticks) butter
2 cups packed brown sugar
1/2 cup light or dark corn syrup
1 teaspoon salt
1/2 teaspoon baking soda
1 teaspoon vanilla
6 quarts popped popcorn

Melt butter, stir in brown sugar, corn syrup and salt.  Bring to boil while stirring constantly; boil without stirring 5 minutes.  Remove from heat, stir in soda and vanilla.  Pour over popped popcorn, mixing well.  Line 2 cookie sheets with parchment paper and divide the mixture between the pans.  Bake at 250 degrees for 1 hour, stirring every 15 minutes.  Remove from oven and cool completely.  Break into pieces and store in tightly covered container.  Makes 6 quarts.