Instructions:
Prepare the cookies:
In a medium saucepan (or in a bowl in the microwave on 50% power), melt the butter and chocolate, stirring frequently. Once melted, set aside and let cool slightly.
In a medium bowl, whisk together flour, cocoa powder, baking powder and salt.
In the bowl of an electric mixer, beat sugar, eggs and vanilla on low speed until fluffy.
Add the cooled chocolate mixture and beat until smooth.
While stirring, slowly add the flour mixture and whisk until well combined.
Scrape the dough down the sides of the bowl, cover and place in the refrigerator for at least 1 hour. The dough should be elastic. If making the dough a day ahead, let it rest at room temperature for 30 minutes before shaping.
Preheat oven to 325*F. and line two baking sheets with parchment paper or a layer of Silpat. Scoop the dough with a spoon (or cookie scoop), then roll it out between the palms of your hands. Place the balls about 5 cm apart on a baking sheet and flatten them slightly.
Bake the cookies for about 12 minutes.
While the cookies are baking, cut a large marshmallow in half (crosswise). When cookies are done, remove from oven and press one marshmallow half (cut side down) into the center of each cookie. Return the cookies to the oven and bake for another 2 to 3 minutes. Let the cookies cool for a few minutes, then transfer them to a wire rack to cool.
Prepare the cookie icing:
Prepare the cookie frosting by whisking all ingredients together in a medium bowl. Place a cooling rack (with the cookies on top) on the baking sheet (to catch excess icing). Put a small amount of icing on each marshmallow and spread a little with the back of a spoon. After frosting some cookies, sprinkle them with sprinkles before the frosting dries.
Let the frosting set for 30 minutes before serving.
