Line two sheet pans with parchment paper or silicone mats.

Whisk the wet ingredients. In a large bowl, whisk the melted butter with the granulated and brown sugars until glossy and combined. Add the egg and vanilla, whisking until smooth.

Combine the dry ingredients. In a separate bowl, whisk the flour, cocoa powder, baking soda, baking powder, and salt to break up any lumps.

Make the dough. Add the dry ingredients to the wet. Switch to a spatula and fold until just combined.

Stir in the chocolate chips. The dough will be thick but scoopable.

Portion the dough. Scoop 2-tablespoon mounds (about 40–45 g each). Roll each into a ball, then flatten gently into a thick disk in your palm.

Add the fluff. Spoon about 1 to 1.5 teaspoons of marshmallow fluff onto the center of each disk.

Try to keep it in a neat dollop to avoid oozing.

Seal well. Fold the dough edges up and over the fluff, pinching to seal fully. Roll back into a ball and place seam-side down on the baking sheet, leaving 2 inches between cookies.

Bake. Bake 9–11 minutes, until the edges are set and the tops are slightly crackled. A little puff is good; they’ll settle as they cool.

If using, sprinkle a pinch of flaky sea salt on hot cookies.

Cool. Let cookies rest on the pan for 10 minutes before transferring to a rack. This helps the centers set without losing their gooey texture.

Serve. Enjoy warm for the best marshmallow pull. They’re still great at room temp—soft, fudgy, and rich.