01 -
Preheat oven to 350°F. Line two baking sheets with parchment paper or silicone mats. Measure all ingredients for efficient assembly.
02 -
Whisk flour, cocoa powder, baking soda, and salt in a medium bowl to ensure even distribution and remove lumps.
03 -
Using a hand or stand mixer, beat softened butter, granulated sugar, and brown sugar until pale and fluffy, about 2-3 minutes.
04 -
Add egg and vanilla extract to the creamed mixture, mixing until fully combined. Scrape bowl sides as needed.
05 -
Gradually add dry ingredients in 2-3 batches, mixing on low speed just until blended to avoid toughness.
06 -
Gently fold semi-sweet chocolate chips into the dough to distribute evenly without breaking them.
07 -
Fold in mini marshmallows and optional marshmallow fluff carefully to maintain visible streaks for swirl effect.
08 -
Using a cookie scoop or tablespoon, space dough balls 2 inches apart on baking sheets. Bake 8-10 minutes until edges are set but centers remain soft.
09 -
Allow cookies to cool on baking sheets 5 minutes before transferring to wire rack to finish cooling and firm up.