• In the bowl of a stand mixer fitted with a paddle attachment, whip the butter for 2 minutes till light. Add both sugars and mix again for 2-3 minutes. Add the egg, vanilla, and milk and mix again till mixed well.
• In a separate bowl, combine the flour, corn starch, cocoa powder, hot cocoa mix, baking soda, salt, and freeze-dried mini marshmallows.
• Add the dry ingredients into the mixing bowl and mix till just combined.
• Refrigerate the dough for 2 hours or up to 2 days. Wrap it well in plastic wrap before refrigerating.
• About 30 minutes before you plan to bake the cookies, preheat the oven to 350 F and line a few baking sheets with parchment paper.
• Roll the dough into about 2 tablespoon-sized balls (about 40 g, if weighing) and place about 3-4 inches apart on the baking sheet.
• Bake the cookies for about 9 minutes, remove from oven and press a half a marshmallow on top of the cookie and bake for an additional 2 1/2 minutes until melty but not browning.
• If your marshmallows are too puffy you can flatten them slightly with a spoon when they come out of the oven.
• Allow to cool 10-12 minutes before transferring to a wire cooling rack to finish cooling.

For the chocolate topping

• In a double boiler, melt the chocolate chips till smooth. Alternatively, you can melt them in the microwave on 50% power in 30-second increments.
• Top the cookies with a spoonful of melted chocolate and cover the marshmallow on top. Let sit for 10 minutes to let the chocolate set a bit before serving.
• Let the chocolate set all the way before placing in an airtight container to store for up to 4 days. See tips for further storage.