Prepare the Cookie Dough:

In a large mixing bowl, cream the butter, granulated sugar, and brown sugar until light and fluffy. Add the eggs, one at a time, beating well after each addition. Mix in the vanilla extract.

In a separate bowl, whisk together the flour, cocoa powder, baking soda, and salt. Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Chill the dough in the refrigerator for 30 minutes to make it easier to handle.

Assemble the Cookies:

Preheat your oven to 350°F (175°C) and line baking sheets with parchment paper. Scoop about 2 tablespoons of dough and flatten it slightly in your hand. Place a marshmallow half (or a few mini marshmallows), a few chocolate chunks, and a few nuts in the center. Take another tablespoon of dough, flatten it, and place it over the filling. Seal the edges, rolling the dough gently into a ball to encase the filling completely.

Place the cookies on the prepared baking sheets, spacing them about 2 inches apart.

Bake the Cookies:

Bake for 10-12 minutes, or until the edges are set but the centers look slightly soft. Let the cookies cool on the baking sheets for 5 minutes before transferring them to a wire rack to cool completely.

Add the Finishing Touches:

If desired, drizzle the cooled cookies with melted chocolate and sprinkle with additional chopped nuts for a beautiful and indulgent finish.