Melt together the butter and chocolate chips in a small sauce pan over medium heat, stirring occasionally. Set aside and let the chocolate cool for about 15 minutes.
In a large bowl combine the dry ingredients (The flour, cocoa powder, baking powder, and salt) whisk them together, and set the bowl aside.
In a large mixing bowl cream together the brown sugar, eggs and vanilla until smooth.
Add the slightly cooled, melted chocolate mixture to the egg mixture and stir until combined.
Slowly add in the dry ingredients while stirring until mixed.
Cover the bowl tightly with plastic wrap or a lid and refrigerate for 1-2 hours (The dough is like a thick cake batter before refrigerated, so you'll need it to firm up a good amount).
Preheat the oven to 325 degrees Fahrenheit and line a baking pan or two with parchment paper.
Roll the dough into 1 1/2 -2 inch cookie dough balls and place onto the prepared baking sheet, at least a couple inches apart.
Bake for 10 minutes, until the cookies start to crack.
Meanwhile, cut the marshmallows in half and cut the chocolate into 1/2 inch pieces.
Remove the cookie sheet from the oven and top each cookie with a piece of chocolate and then half a marshmallow (sticky side down) and cook for another 3-4 minutes until the marshmallow is puffed and gooey.
Remove from the pan and let the cookies cool on the pan for about 5 minutes.
Sprinkle grated chocolate over the top of your marshmallows if desired.
Transfer to a cooling rack to cool longer, or eat the cookies warm (recommended).