In a medium bowl, whisk together the all-purpose flour, Dutch-process cocoa powder, hot cocoa mix packets, baking soda, and fine sea salt until evenly blended and lump-free. Set aside.

In a large mixing bowl, whisk together the melted butter, dark brown sugar, and granulated sugar until glossy and cohesive. Whisk in the eggs and vanilla extract vigorously for 1 minute until slightly pale and thickened.

Add the dry flour-cocoa mixture to the wet ingredients. Fold with a silicone spatula just until a soft, fudgy chocolate dough forms. Fold in 3/4 cup of the chocolate chips, reserving 1/4 cup for topping.

Cover the bowl with plastic wrap and chill in the refrigerator for 30 minutes to firm up slightly for easier shaping.

Preheat your oven to 350°F (175°C) and line two large baking sheets with parchment paper.

Scoop 2 tablespoons of chilled dough, flatten into a disc in your palm, place two marshmallow halves (or 1 full marshmallow cut in half) in the center, and wrap the chocolate dough completely around the marshmallow, sealing tightly so it does not leak during baking.

Place the dough balls 2 inches apart on prepared baking sheets. Press a few reserved chocolate chips into the tops of each dough ball.

Bake for 9 to 11 minutes until the edges are just set and the cookies are puffed with crackled tops. Do not overbake!

Remove from the oven. If a marshmallow peeked out, use a round cookie cutter or glass to gently swirl around the warm cookie to reshape it into a perfect circle. Cool on the pan for 5 minutes, then transfer to a wire rack to enjoy warm and gooey!