Preheat the oven to 350 degrees F. Line two baking sheets with parchment paper. Set aside.
In a medium bow, whisk together the flour, hot chocolate mix, salt, and baking soda. Set aside.
In the bowl of a stand mixer, cream the butter and sugars together. Add the eggs, one at a time, mixing well between additions. Add the vanilla extract and mix until combined.
Little by little, add the dry ingredients to the wet, until everything is well combined. Scrape down the sides of the bowl as needed. Mix in the chocolate chips and marshmallow bits.
Using a cookie scoop, drop dough by the tablespoon onto the prepared cookie sheets. Bake for 14 minutes, or until the edges are firm.
Allow the cookies to cool on the sheet for 5 minutes before removing them to a wire rack to finish cooling completely.