01 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
02 - In a medium bowl, whisk together flour, cocoa powder, baking soda, and salt.
03 - In a large bowl, cream softened butter with brown sugar and granulated sugar until light and fluffy using an electric mixer or whisk.
04 - Beat in eggs one at a time, then add vanilla extract. Mix until smooth.
05 - Gradually add the dry mixture to the wet mixture, mixing just until combined.
06 - Fold chocolate chips, chopped nuts, and 3/4 cup mini marshmallows into the dough.
07 - Scoop rounded tablespoons of dough onto prepared baking sheets, spacing each 2 inches apart.
08 - Lightly press extra marshmallows and festive sprinkles onto the tops of each portion.
09 - Bake for 10 to 12 minutes until edges are set but centers remain soft.
10 - Let cookies cool on baking sheets for 5 minutes, then transfer to a wire rack to cool completely.