Preheat your oven to 350°F (175°C).

Line two baking sheets with parchment paper and set them aside.

In a large bowl, cream the room-temperature butter and brown sugar together until the mixture is light and fluffy.

Add the dry hot cocoa mix, instant coffee or espresso powder (if using), large eggs, and vanilla extract to the creamed butter mixture.

Stir the ingredients until they are smooth and well combined.

Gradually mix in the all-purpose flour and baking soda until no dry pockets of flour remain. Be careful not to overmix the dough.

Fold in the chocolate chips gently until they are evenly distributed throughout the dough.

Scoop approximately 2 tablespoons of dough for each cookie onto the prepared baking sheets, ensuring to space the cookies well apart (about 6 cookies per sheet).

Bake the cookies for 10–11 minutes, or until their edges are set and lightly golden, but the centers still appear soft.

Immediately after removing the cookies from the oven, gently press the back of a spoon into the center of each hot cookie to create a small indentation.

Press a few mini marshmallows into the indentation of each hot cookie.

Allow the cookies to cool on the baking sheet for 5 minutes to set.

Carefully transfer the cookies to a wire rack to cool completely.

Once the cookies are completely cooled, drizzle them with melted chocolate.

Optionally, top the drizzled chocolate with sprinkles if desired.