Preheat the oven to 350 degrees F.
In a large bowl combine the flour, cocoa powder, baking soda and salt.
In a separate mixing bowl, blend the butter with the sugar, vanilla and butter until smooth (I used a hand held mixer or stand up mixer for this).
Add in the eggs 1 at a time until thoroughly combined.
Then hand mix in the dry ingredients into the wet ingredients. Do not over mix.
Scoop approximately 1 Tbsp of the dough onto a baking sheet and ensure that they are approximately 2 in a part.
Bake for 8-10 minutes until the edges of the cookies are set and middle is still soft.
Place a marshmallow in the center of each cookie and press them down slightly.
Bake for another 2-3 minutes to melt the marshmallow slightly.
Transfer the cookies to a cool rack and allow them to cool completely.
Dust some cocoa powder over the top of the cookies for decoration.
Enjoy!