Pop corn according to package instructions (*see note).
In a medium saucepan over medium heat, MELT butter; STIR in brown sugar, syrup and salt
Bring to a BOIL, STIRRING constantly; let BOIL for 4 minutes without stirring
REMOVE from heat; quickly STIR in baking soda and vanilla (mixture will foam up); STIR mixture down.
TRANSFER popped corn to a large mixing bowl; ADD peanuts if desired to make this like Cracker Jacks®.
Using a large spoon greased with butter, carefully STIR and TOSS popcorn while adding hot mixture until all kernels are coated.
SPREAD the coated popcorn in a shallow baking pan.
BAKE in 250° oven for 1 hour, STIRRING every 15 minutes with a non-stick spatula.
REMOVE from oven; COOL completely; BREAK into pieces.
Put the leftover caramel corn in a sealed bowl and enjoy over several days.
A typical microwave package yields 2 1/2 quarts when popped. Use two packages and just eat the remaining popcorn as is.
Per Serving (excluding unknown items): 2657 Calories; 204g Fat (65.9% calories from fat); 60g Protein; 178g Carbohydrate; 22g Dietary Fiber; 248mg Cholesterol; 2068mg Sodium. Exchanges: 2 1/2 Grain(Starch); 7 1/2 Lean Meat; 36 1/2 Fat; 9 1/2 Other Carbohydrates.