In a double boiler, melt the butter and chocolate, stirring frequently. Once melted, set aside to cool
In a medium bowl, whisk together the flour, cocoa powder, baking powder and salt.
In a standing mixer, beat the sugar, eggs and vanilla on low speed until combined.
Add the cooled chocolate and mix until combined
Gradually add in the flour ingredients and mix until combined
Scoop the dough (Will be brownie like texture) into a bowl and cover with foil and place into the fridge for 4 hours.
Preheat oven to 325 degrees and line a cookie sheet with parchment paper.
Using a small ice cream scoop, scoop some batter into your hands and roll into a ball
Place cookies about 2 inches apart
Bake the cookies for about 10 minutes
While cookies are baking, cut the marshmallows in half
Once cookies are baked, place a marshmallow into the center of the cookies and lightly press down
Place cookies back into the oven for another 2-3 minutes
Place a wire rack over another cookie sheet to allow the icing to drip off
Once cookies are done baking let cool for a few minutes before transferring to a wire rack while you make the icing