Instructions
Place the butter and chopped chocolate in a heat safe bowl, and microwave in 30 second intervals, stirring frequently until chocolate is melted and mixture is smooth. Let cool for 15 minutes.
In a medium bowl, whisk together the flour, cocoa powder, baking powder, and salt.

In a large bowl with an electric mixer, beat the sugar, eggs and vanilla on low speed until smooth. Mix in the cooled chocolate mixture just until blended. Add the flour mixture in 2 batches, mixing until just combined. (The dough will be thick and sticky like brownie texture.)

Cover and refrigerate the dough for at least 1 hour. (Note: If you chill for more than 4 hours, allow the dough to sit at room temperature for about 30 minutes before shaping.)
Preheat the oven to 325 degrees. Line baking sheets with parchment paper.

Form tablespoon-sized balls of the chilled dough with a cookie scoop and drop them 2-inches apart on the prepared baking sheets.
Bake the cookies for about 10-12 minutes until they're crackled on top.
Remove cookies from the oven and gently press one marshmallow half (cut side down) onto the top of each cookie in the center.

Place cookies back into the oven until the marshmallows start to soften, about 3 minutes.
Remove from oven and let cool for about 5 minutes, then transfer them to a wire rack to cool completely.

Prepare the icing: Whisk all the icing ingredients together in a medium bowl. Place wire cooling rack (with cookies on it) over a baking sheet (to catch any excess icing). Spoon a small amount of icing onto the top of each marshmallow, and use the back of the spoon to spread it a bit. After icing just a couple cookies, top with sprinkles before the icing dries.

Allow icing to set and dry completely, 30-60 minutes, before serving.
Enjoy with a glass of milk or hot cocoa!