Cream together butter, granulated sugar, and brown sugar until light and fluffy in a big bowl.

Beat in eggs and vanilla extract until well combined.

In another bowl, whisk together flour, baking soda, salt, hot cocoa mix, and cocoa powder.

Gradually add dry ingredients to wet ingredients, mixing until just combined.

Stir in milk until the dough is thick and slightly sticky.

Cover and chill dough for at least 2 hours.

Heat the oven up to 350°F (177°C). Line baking sheets with parchment paper or silicone baking mats.

Scoop dough onto prepared baking sheets, leaving space between each cookie.

Bake for 10 minutes. Then, press a marshmallow half into each cookie.

Bake again for 2-3 minutes more or until marshmallows are puffed.

Gently press down on marshmallows with the back of a spoon.

Cool on a baking sheet for 10-15 minutes before transferring to a wire rack to cool completely.

Melt chopped chocolate in a double boiler or microwave.

Drizzle melted chocolate over cooled cookies.

Let the chocolate set completely.

Store in an airtight container at room temperature or in the freezer.