Preheat the oven to 350°F (175°C) and line a baking sheet with parchment paper.

In a mixing bowl, cream together the softened butter, brown sugar, and granulated sugar until light and fluffy.

Add the eggs one at a time, mixing well after each addition, then stir in the vanilla extract.

In another bowl, whisk together the flour, cocoa powder, baking soda, and salt.

Gradually add the dry ingredients to the wet ingredients, mixing until just combined.

Using a cookie scoop, take a portion of the cookie dough and flatten it in your palm.

Place a teaspoon of Nutella and a few mini marshmallows in the center, then wrap the dough around the filling to form a ball.

Place the stuffed cookie balls on the prepared baking sheet, spacing them about 2 inches apart.

Bake in the preheated oven for 10-12 minutes, or until the edges are set but the centers are still soft.

Remove from the oven and let the cookies cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.