01 -
Preheat oven to 350°F. Line two baking sheets with parchment paper or silicone mats to prevent sticking.
02 -
In a medium bowl, whisk together flour, cocoa powder, baking soda, and salt until evenly mixed with no lumps.
03 -
Using a hand or stand mixer, beat softened butter, granulated sugar, and brown sugar until light and fluffy, approximately 2 to 3 minutes.
04 -
Beat in egg and vanilla extract until fully combined, scraping down bowl sides as needed.
05 -
Gradually add dry ingredients to wet mixture in 2 to 3 additions, mixing on low speed until just combined to avoid toughness.
06 -
Gently fold semi-sweet chocolate chips into the dough ensuring even distribution.
07 -
Carefully fold mini marshmallows and optional marshmallow fluff into dough, preserving streaks to create swirl effect without overmixing.
08 -
Scoop dough onto prepared sheets using a cookie scoop or tablespoon, spacing cookies about 2 inches apart. Bake 8 to 10 minutes until edges are set but centers remain slightly soft.
09 -
Allow cookies to cool on baking sheets for 5 minutes before transferring to a wire rack to finish cooling and firm up.