, beat the butter, granulated sugar, and brown sugar together on medium high speed until fluffy and light in color, about 2–3 minutes.

, and then beat on high speed until combined. Scrape down the sides and bottom of the bowl as needed.

, whisk the flour, cocoa powder, hot cocoa mix, baking soda, and salt together until combined. Add the dry ingredients to the bowl with the wet ingredients. Beat on low until combined. The cookie dough will be quite thick. Finally, beat in the milk. The cookie dough will be thick and sticky.

Chilling is imperative for this sticky cookie dough.

Line large baking sheets with parchment paper or silicone baking mats. Set aside.

Scoop and roll dough, a heaping 1 Tablespoon (about 25-26g) each, into balls. Arrange 2–3 inches apart on the baking sheets.

Remove the cookies from the oven and lightly press a marshmallow half into the tops of each cookie. Return them to the oven and bake for 2 more minutes. Remove from the oven and, using the back of a spoon, gently press down on the marshmallow to slightly flatten it out.

, and then transfer cookies to a wire rack to cool completely.

You can melt the chocolate in a double boiler or the microwave. If using the microwave, place the chopped chocolate in a medium heat-proof bowl. Microwave for 20-second increments, stirring after each increment until completely melted and smooth. Spoon melted chocolate over each cooled marshmallow-topped cookie. Chocolate sets at room temperature in 30-60 minutes. Once chocolate has set, you can stack, store, transport, and gift the cookies.