Place 10 cups of popped popcorn in a very large mixing bowl. Remove and discard any unpopped kernels. If needed, divide popcorn between two bowls to make tossing easier.
10 cups popped popcorn
Sprinkle 1 cup of mini marshmallows evenly over the popcorn so you get little gooey bites throughout. Set the bowl aside.
1 cup mini marshmallows
In a medium microwave-safe bowl, combine the semisweet chocolate chips and unsalted butter. Microwave on 50% power for 30 seconds, stir well, then continue heating in 20–30 second bursts at 50% power, stirring after each, until mostly melted. Stir until completely smooth and glossy. Alternatively, melt together in a small saucepan over very low heat, stirring constantly.
1 cup semisweet chocolate chips, 3 tablespoons unsalted butter
While the chocolate mixture is still warm, whisk in the unsweetened cocoa powder, hot cocoa mix, 2–3 tablespoons powdered sugar (start with 2), vanilla extract, and fine sea salt. Whisk until fully blended and no dry streaks remain. If the mixture is too thick to drizzle, microwave for 10–15 seconds at 50% power and stir again until pourable.
2 tablespoons unsweetened cocoa powder, 2 tablespoons hot cocoa mix, 2-3 tablespoons powdered sugar, 1 teaspoon vanilla extract, 1/4 teaspoon fine sea salt
Slowly pour the warm hot cocoa chocolate mixture over the popcorn and marshmallows. Use a large spatula or clean hands to gently toss until as many pieces as possible are coated, being careful not to crush the popcorn. Some larger clumps are fine.
10 cups popped popcorn, 1 cup mini marshmallows, 1 cup semisweet chocolate chips, 3 tablespoons unsalted butter, 2 tablespoons unsweetened cocoa powder, 2 tablespoons hot cocoa mix, 2-3 tablespoons powdered sugar, 1 teaspoon vanilla extract, 1/4 teaspoon fine sea salt
Line a large baking sheet (or two smaller baking sheets) with parchment paper. Spread the coated popcorn out in an even layer, breaking up any very large mounds so it can cool and set more quickly.
Place the white chocolate chips in a microwave-safe bowl. Microwave on 50% power in 20-second bursts, stirring after each, until melted and smooth. Use a spoon to drizzle the melted white chocolate in a zigzag pattern over the popcorn.
1/2 cup white chocolate chips
While the chocolate is still slightly warm, sprinkle extra mini marshmallows, crushed candy canes, mini chocolate chips, chocolate sprinkles, or a light dusting of cocoa powder/hot cocoa mix over the popcorn. Gently press larger toppings like marshmallows so they adhere.
Crushed candy canes or peppermint candies, Mini chocolate chips or chocolate sprinkles, Extra mini marshmallows, Extra cocoa powder or hot cocoa mix
Let the popcorn sit at room temperature for 20–30 minutes, or until the chocolate is firm to the touch. Break into clusters and transfer to a serving bowl. If desired, lightly dust with a teaspoon or two of powdered sugar or hot cocoa mix just before serving.