In a large mixing bowl, beat 1 stick of softened unsalted butter with ½ cup granulated sugar and ½ cup dark brown sugar until light and fluffy, about 3 minutes. Add 1 egg and 1 teaspoon of vanilla extract, mixing until creamy.

In a separate bowl, whisk together 1 ¾ cups all-purpose flour, ½ cup natural cocoa powder, 1 package of dry hot cocoa mix, 1 teaspoon baking soda, and ½ teaspoon salt. Ensure no lumps remain.

Gradually incorporate the dry ingredients into the wet mixture until just combined. Cover and chill for 2 to 3 hours.

Preheat oven to 350°F (175°C) and line a baking sheet with parchment paper. Scoop tablespoon-sized balls of chilled dough onto the sheet, leaving 2 inches apart. Bake for 10 minutes.

After 10 minutes, press halved marshmallows cut side down into the center of each cookie. Bake for an additional 2 minutes.

Let cookies cool on the baking sheet for 10 minutes. Melt ½ cup of semi-sweet chocolate and drizzle over cooled cookies before transferring to a wire rack.