01 - Preheat oven to 350°F and line two baking sheets with parchment paper.
02 - In a medium bowl, whisk together flour, cocoa powder, baking soda, and salt to evenly distribute.
03 - In a large bowl, beat unsalted butter, brown sugar, and granulated sugar until mixture is pale and fluffy.
04 - Incorporate eggs one at a time, followed by vanilla extract, mixing until smooth and homogenous.
05 - Gradually mix in the dry ingredients to the wet base, stirring just until a cohesive dough forms.
06 - Fold in chocolate chips, chopped nuts, and 3/4 cup mini marshmallows until evenly distributed.
07 - Scoop rounded tablespoons of dough onto prepared baking sheets, spacing at least 2 inches apart.
08 - Gently press remaining marshmallows and festive sprinkles onto each dough mound.
09 - Bake for 10 to 12 minutes, until edges are set and centers retain a soft texture.
10 - Allow cookies to cool for 5 minutes on the baking sheets, then transfer to a wire rack until completely cooled.