Step 1: Preparing the Dough

1. Cream together the butter, granulated sugar, and brown sugar until light and fluffy (about 2–3 minutes).
2. Mix in the egg and vanilla extract until fully combined.

Step 2: Mixing Dry Ingredients

1. In a separate bowl, whisk together the flour, cocoa powder, hot cocoa mix, baking soda, and salt.
2. Gradually add the dry ingredients to the wet mixture, mixing on low speed.
3. Add milk and mix until the dough comes together (it will be thick and sticky).

Step 3: Chilling the Dough

1. Cover the dough and refrigerate for at least 2 hours or up to 3 days.

Step 4: Shaping and Baking

1. Preheat the oven to 350°F (177°C) and line baking sheets with parchment paper.
2. Roll dough into 1-tablespoon-sized balls and place them 2–3 inches apart on the prepared baking sheets.
3. Bake for 10 minutes.
4. Remove from the oven and press a marshmallow half onto each cookie.
5. Return cookies to the oven for an additional 2 minutes.

Step 5: Adding the Chocolate Topping

1. Melt the semi-sweet chocolate in 20-second microwave increments, stirring in between.
2. Spoon melted chocolate over the marshmallow-topped cookies.
3. Let the chocolate set at room temperature for 30–60 minutes