Creating Thick Nutella Marshmallow Cookies with Fudgy Layers can be straightforward if you follow these simple steps:

1. Preheat Oven: Begin by preheating your oven to 350°F (175°C). Line a baking sheet with parchment paper.

2. Cream Butter and Sugar: In a large bowl, cream together the softened butter and granulated sugar until light and fluffy.

3. Add Nutella and Egg: Stir in the Nutella, and then beat in the egg and vanilla extract until well combined.

4. Mix Dry Ingredients: In another bowl, whisk together the flour, cocoa powder, baking soda, and salt.

5. Combine Mixtures: Gradually add the dry mixture to the wet ingredients, mixing until just combined. Be careful not to overmix.

6. Fold in Chocolate Chips and Marshmallows: Gently fold in the semi-sweet chocolate chips and mini marshmallows, ensuring an even distribution throughout the dough.

7. Scoop the Dough: Using a cookie scoop or tablespoon, drop heaping mounds of dough onto the prepared baking sheet, spacing them about 2 inches apart.

8. Bake: Place the baking sheet in the preheated oven and bake for 15-20 minutes. The edges should be set, but the centers may appear slightly underbaked.

9. Cool: Remove the cookies from the oven and allow them to cool on the baking sheet for 10 minutes before transferring them to a wire rack to cool completely.

10. Enjoy: Once cooled, these cookies are ready to be devoured!