Step 1: Prepare the Dough
In a large bowl, cream together the softened butter, brown sugar, and granulated sugar until light and fluffy—about 2–3 minutes. Beat in the eggs one at a time, then add vanilla extract.

Step 2: Mix Dry Ingredients
In a separate bowl, whisk together the flour, baking soda, and salt. Gradually add the dry ingredients to the wet mixture, mixing just until combined.

Step 3: Fold in the Goodies
Use a spatula to gently fold in the chocolate chips and mini marshmallows. For a stronger swirl effect, reserve a handful of marshmallows to press into the tops of the cookies before baking.

Step 4: Scoop and Chill
Scoop the dough into 2-tablespoon balls and place on a lined baking sheet. Chill the dough for 30 minutes to help control spreading.

Step 5: Bake to Perfection
Preheat the oven to 350°F (175°C). Bake the cookies for 10–12 minutes or until the edges are golden and the centers look just set. Remove from the oven and let them cool on the pan for 5 minutes before transferring to a wire rack.

Step 6: Enjoy the Swirls
Watch as the gooey marshmallow forms beautiful swirls across the surface of each cookie, blending perfectly with the melted chocolate.