Creating Chocolate Marshmallow Swirl Cookies can be straightforward when you follow these simple steps:

1. Preheat Oven: Preheat your oven to 350°F (175°C). Line a baking sheet with parchment paper.
2. Cream Butter and Sugar: In a large mixing bowl, cream together the softened butter and granulated sugar until light and fluffy.
3. Add Eggs and Vanilla: Beat in the eggs, one at a time, followed by the vanilla extract until well combined.
4. Combine Dry Ingredients: In a separate bowl, sift together the flour, cocoa powder, baking soda, and salt.
5. Mix Dry with Wet: Gradually add the dry mixture to the wet ingredients, mixing until fully incorporated.
6. Fold in Marshmallows and Chips: Gently fold in the mini marshmallows and chocolate chips if using.
7. Scoop Dough: Using a cookie scoop or tablespoon, drop rounded balls of cookie dough onto the prepared baking sheet, spacing them about 2 inches apart.
8. Add Marshmallow Swirls: Place a few additional marshmallows on top of each cookie, pressing them down slightly to create swirls as they bake.
9. Bake: Bake in the preheated oven for 10-12 minutes or until the edges are set, but the centers still appear slightly soft.
10. Cool: Remove from the oven and allow cookies to cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.

With these easy instructions, you will produce amazing Chocolate Marshmallow Swirl Cookies that will impress anyone who takes a bite!