Preheat your oven to 350°F (175°C) and prepare your baking sheets with parchment paper or a silicone mat.

In a large mixing bowl, cream together softened butter, granulated sugar, and brown sugar until light and fluffy, about 3-5 minutes.

Beat in the eggs one at a time, then add vanilla extract, mixing until smooth.

In a separate bowl, whisk together all-purpose flour, cocoa powder, baking soda, and salt.

Gradually add the dry mixture to the wet mixture and stir until just combined.

Gently fold in mini marshmallows, ensuring they are evenly distributed.

Scoop generous portions of the dough onto prepared baking sheets, spacing them about 2 inches apart.

Bake for 10-12 minutes, or until the edges are firm but the centers remain soft.

Let cool on the baking sheet for 5 minutes before transferring to a wire rack.

Serve and enjoy your Chocolate Marshmallow Swirl Cookies, ideally with milk or coffee!