Preheat oven to 325 degrees. Line 2 large cookie sheets with parchment paper. Set aside.
In a medium saucepan set to medium heat, add butter and chocolate chips, stirring frequently. Once melted and smooth, stir in hot cocoa powder and allow it to melt it, it will not melt completely and this is okay. Remove from heat and allow to cool slightly.
In a medium-sixes bowl, toss together the flour, dark cocoa powder, baking powder and salt.
In the bowl of your stand mixer fitted with the paddle attachment OR hand mixer, beat the brown sugar, eggs and vanilla at low speed until smooth for about 2 minutes. Stir in the warm chocolate mixture until just combined. Gradually pour in the flour mixture on low speed until just incorporated. Don't over-mix. Refrigerate the dough for at least 1 hour s it is firm enough to scoop. You can make the dough a day ahead, just allow it to sit at room temperature for 30 minutes before shaping so it's easier to scoop and roll.
Scoop and roll the dough to form 1" balls and arrange 2 inches apart on each cookie sheet. Bake until the tops of the cookies start to crack on top, 10-12 minutes.
Meanwhile, cut all mini candy bars in half (you should have two rectangles together for each cookie) and set aside. Gather 5 mini marshmallows, press them down with the palm of your hand so they stick together and place them on top of each chocolate piece. It's easier to get this step prepared before the cookies come out of the oven. You will want one for each cookie.
Remove the cookie from the oven and gently press one set of chocolate/marshmallows on top of each cookie. Place them back into the oven until the marshmallows are puffy and soft, about 4 minutes. Allow the cookies to cool for 5 minutes on the pans before moving to a wire rack to finish cooling completely.
When cookies are cool, melt chocolate chips in small bowl until smooth. Drizzle on top of cookies and serve.