01 - 
                In a medium bowl, whisk together all-purpose flour, cocoa powder, baking soda, and salt until evenly combined.
              
              
              
                02 - 
                Using an electric mixer, beat unsalted butter and granulated sugar in a large bowl until pale and fluffy, approximately 3 to 4 minutes.
              
              
              
                03 - 
                Beat in eggs one by one, ensuring each is fully incorporated before adding the next. Stir in vanilla extract until evenly distributed.
              
              
              
                04 - 
                Gradually add the dry mixture to the wet ingredients, mixing on low speed until just combined. Avoid overmixing for best texture.
              
              
              
                05 - 
                Gently fold marshmallow fluff into the dough to create visible swirls, or reserve for after chilling as preferred.
              
              
              
                06 - 
                Cover the dough and refrigerate for at least 60 minutes to make it easier to handle and reduce spreading during baking.
              
              
              
                07 - 
                Preheat oven to 175°C. Line two baking trays with parchment paper or silicone baking mats.
              
              
              
                08 - 
                Scoop out dough and roll into balls. Place on prepared trays, spacing 5 cm apart. Press an indent into each and add one teaspoon of marshmallow fluff. Swirl the fluff into the dough using a toothpick.
              
              
              
                09 - 
                Bake for 10–12 minutes, or until set at the edges but soft in the center. For extra gooeyness, add more marshmallow fluff halfway through baking if desired.
              
              
              
                10 - 
                Allow cookies to cool on the baking tray for 5 minutes. Transfer to a wire rack to cool completely for best texture.