Preheat your oven to 120 C (250 F) and line a baking sheet with parchment paper.
Over medium high heat in a sauce pan, combine brown sugar, butter, water and corn syrup. Bring the temp up 121 C (250 F), use a probe thermometer. Remove from heat when the temp is reached.
Add the vanilla extract and baking soda, stir to incorporate into mixture.
In a large bowl, add the popped popcorn, drizzle the cooked mixture over popcorn, mix with wooden spoon or spatula, add the peanuts and stir to distribute evenly.
Transfer combined popcorn mixture onto the baking sheet, distribute to make an even layer.
Bake in oven for 1 hour, however, after 20 minutes, remove and stir popcorn mixture, then bake for an additional 20 minutes, remove and stir, then bake for the remaining 20 minutes.
Remove from oven and allow to cool. There, you just made Cracker Jack.
Once the Cracker Jack is cool, store in an airtight container or enjoy.