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

In a large mixing bowl, combine butter, granulated sugar, and brown sugar, and cream together for 3-4 minutes until light and fluffy.

Add eggs one at a time, mixing well after each. Stir in vanilla extract.

Whisk together flour, cocoa powder, baking soda, and salt in a separate bowl.

Gradually mix dry ingredients into the butter mixture until just combined.

Fold in chocolate chips and mini marshmallows using a spatula.

Scoop rounded balls of dough onto prepared baking sheets, leaving space between each.

Bake for 10-12 minutes, watching for edges to set while centers remain soft.

Allow cookies to cool on the baking sheets for 5 minutes before transferring them to cooling racks.

Dust with powdered sugar before serving, if desired.