Spray 8 wells of a muffin tin generously with cooking spray (or use a loaf pan if you don’t have a muffin tin).

In a large saucepan over low heat, melt the 5T of butter and the marshmallows, stirring constantly until completely melted and well-mixed.

Remove from heat and stir in the 3c plain popcorn, mixing until all popcorn is completely covered.

Press mixture into prepared loaf pan, smoothing the top. Set aside and let cool completely. Once cool, break up with your hands into 1/2T-sized pieces.

Preheat oven to 350°F. Line two cookie sheets with parchment paper or Silpat liners.

In the bowl of a stand mixer fitted with the paddle attachment, cream together butter, sugar, and hot chocolate, mixing on high for 2-3 minutes until well-combined and beginning to get fluffy. Scrape the bowl and paddle.

Add the egg and vanilla, and beat on high for another 7-8 minutes (for a total of 10 minutes of mixing), stopping once or twice to scrape the bowl and paddle. The mixture should now be lighter in color and very fluffy.

In a separate bowl, combine the flour, cocoa powder, baking soda, baking powder, and salt. Then add to the butter-sugar-egg mixture and beat on low speed just until almost combined (there should be a bit of flour mixture still visible).

Add the buttered popcorn, milk chocolate chips, and white chocolate chips, and mix on low speed just until everything is combined. Remove bowl from mixer and use a rubber spatula to scrape the bowl and finish mixing if there are still flour bits visible.

Using a large cookie scoop (about 1/3 c size), scoop dough onto prepared cookie sheets, leaving about 2” between.

Flatten cookies a bit with your hand, then top with about 1/2T-sized pinch of the Popcorn Marshmallow Treat mixture, pressing it into the dough a bit so it sticks.

Bake for 8-10 minutes, or until cookies no longer look wet and the Popcorn Marshmallow Topping is nicely browned.

Allow to cool on the baking sheet for 5 minutes, then move to a cooling rack to cool completely.