Preheat oven to 350ºF. Spread the peanuts onto a rimmed baking sheet and roast in the oven until fragrant and lightly browned, stirring halfway through, about 15 minutes.

Reduce oven temperature to 250ºF.

Lightly coat a large deep roasting pan with nonstick spray. Dump the popcorn in and roughly spread to an even layer. Sprinkle the roasted peanuts over the top.

In a small saucepan set over medium heat, combine the brown sugar, butter, corn syrup, and salt. Whisk until the sugar is dissolved and the butter is melted - do not let it come to a boil. Cook, stirring, for 2-3 minutes until the sauce is thick and caramelized. Then stir in the baking soda and vanilla.

Evenly pour the caramel sauce over the popcorn and peanuts. Quickly but gently scoop and stir until everything is coated.

Bake at 250ºF for about 35-40 minutes, stirring occasionally, until the popcorn is crisp (the popcorn will continue to crisp up as it cools.)

Transfer the baked Cracker Jack to a large rimmed, parchment lined baking sheet spread to an even layer. Set aside to cool completely, then break apart if necessary.