Preheat your oven to 350°F (175°C).

In a large mixing bowl, cream together the softened butter, granulated sugar, and brown sugar until light and fluffy, about 2-3 minutes.

Add in the eggs and vanilla extract, beating until combined.

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

Gradually add this dry mixture to your wet ingredients, mixing until just combined.

Fold in the chocolate chips, mini marshmallows, and chopped nuts.

Drop spoonfuls of the cookie dough onto a lined baking sheet, spacing them about 2 inches apart.

Bake for 10-12 minutes, until the edges are firm and the centers look slightly soft.

Let the cookies cool on the baking sheet for a few minutes before transferring them to a wire rack to cool completely.