01 -
In a medium bowl, whisk the flour, cocoa powder, baking soda, and salt until evenly combined.
02 -
In a large mixing bowl, use an electric mixer to beat the softened butter with the granulated sugar on medium speed for 3–4 minutes until pale and fluffy.
03 -
Add eggs one at a time, beating well after each addition. Stir in the vanilla extract until thoroughly blended.
04 -
Gradually add the dry ingredients to the wet mixture on low speed, mixing just until combined and a cohesive dough forms. Do not overmix.
05 -
Lightly swirl the marshmallow fluff into the dough using a spatula, or wait to add after chilling depending on preferred swirl texture.
06 -
Cover and refrigerate the dough for at least 1 hour to ensure easier handling and limit spreading during baking.
07 -
Line two baking sheets with parchment paper or silicone baking mats and preheat oven to 350°F (175°C) about 20 minutes before baking.
08 -
Using a cookie scoop or tablespoon, portion the chilled dough and roll into balls. Place on prepared sheets about 2 inches apart. Press a small indent into centers and spoon a teaspoon of marshmallow fluff into each. Swirl the marshmallow gently with a toothpick.
09 -
Bake in the preheated oven for 10–12 minutes until edges are set and centers remain soft. Optionally, add more fluff on top halfway through for extra gooeyness.
10 -
Allow cookies to cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely for optimal texture.