Preheat the oven to 250°F. Line 2 large rimmed baking sheets with parchment paper or silicone baking mats.

Toss together the popcorn, marshmallows, graham crackers, and chocolate chips in a large bowl.

Combine the granulated sugar, butter, brown sugar, and corn syrup in a medium saucepan. Bring to a boil over medium – high, stirring until the butter melts and the ingredients are completely combined.

Continue to boil, without stirring, until a candy thermometer inserted in the mixture registers 245°F (firm ball stage), about 4 minutes.

Remove the sugar mixture from the heat, and stir in the salt and baking soda.

Gradually pour the sugar mixture over the popcorn mixture, stirring gently with a heatproof spatula until the popcorn is evenly coated.

Spread evenly onto the prepared baking sheets.

Bake until the sugar mixture is melted and evenly incorporated, about 20 minutes.

Stirring gently after 10 minutes.

Remove from the oven, and place in a cool, dry place until the chocolate is firm, about 1 hour.