Preheat your oven to 350°F (175°C) and line your baking sheets with parchment paper.

Cream the softened butter, granulated sugar, and brown sugar together until light and fluffy.

Add the egg, milk, and vanilla extract to the creamed mixture and mix on low until fully incorporated.

Whisk together the flour, powdered hot cocoa mix, unsweetened cocoa powder, baking soda, and salt in a separate bowl.

Gradually add the dry ingredients to the wet mixture, mixing on low speed until just combined.

Fold in the marshmallow bits and semi-sweet chocolate chips until evenly distributed.

Drop rounded balls of dough onto prepared baking sheets, spacing them about 2 inches apart.

Bake for 8-10 minutes until the edges are set and the centers look soft but not wet.

Press additional marshmallow bits and chocolate chips onto warm cookies and cool for 5-10 minutes before transferring.