
Preheat oven to 350 degrees. Line half sheet pans with parchment paper. Set aside.
In the bowl of an electric stand mixer fitted with the paddle attachment or in a large bowl using a handheld electric mixer, combine the butter, granulated sugar, brown sugar, baking soda, baking powder, and salt. Mix until well-combined and creamy, 1 to 2 minutes.
Add the eggs and vanilla and mix until well-combined, scraping down the sides of the bowl as needed.
Add the flour, hot cocoa mix, and cocoa powder. Mix until just combined; it's ok if a few dry streaks remain. Add the mini marshmallow bits and chocolate chips and mix on low speed until evenly combined.
Scoop the dough into 2-tablespoon size cookie dough balls (I use a #40 cookie scoop) and roll until smooth. Place several inches apart on the prepared baking sheets.
Bake for 10 to 11 minutes until the cookies are just set around the edges (better to under bake slightly rather than over bake). Let the cookies cool for a minute or two on the baking sheets. Remove to a cooling rack to cool completely (or not...these cookies are insanely delicious eaten warm).