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

In a stand mixer, cream together the butter, granulated sugar, and brown sugar until light and fluffy, about 2-3 minutes. Add eggs one at a time, mixing well.

In a separate bowl, whisk together flour, cocoa powder, baking soda, and salt. Gradually add to wet ingredients, mixing on low until combined.

Gently fold in chocolate chips and mini marshmallows until evenly distributed.

Drop rounded dough balls onto baking sheets, 2 inches apart, and bake for 10-12 minutes until edges are set, but centers remain soft.

Allow cookies to cool on the baking sheet for about 5 minutes before transferring to a wire rack to cool completely.