Bring the butter, sugars, corn syrup, salt and vanilla to a boil. Reduce the heat and let it boil for 5 minutes, stirring occasionally.
Remove from heat and stir in 1 teaspoon baking soda. This will start to "grow" so make sure your saucepan is big enough.
Put the popcorn in a roaster pan. Pour the caramel over the popcorn and stir to mix. Bake in 250 degree oven for 1 hour, stirring every 15 minutes.
After it is done baking, pour the popcorn out onto parchment paper to let it cool.
Store in an airtight container.
Video
Notes
The calories shown are based on the 1 cup of caramel corn. Since different brands of ingredients have different nutritional information, the calories shown are just an estimate.