Begin by placing the semi-sweet baking chocolate and unsalted butter in a medium microwave-safe mixing bowl. Heat this in the microwave using 30-second intervals, stirring well between each interval until melted and smooth. Set aside to cool slightly.

In another medium mixing bowl, sift together the all-purpose flour, unsweetened cocoa powder, baking powder, and salt. Whisk until well combined.

In the electric stand mixer, combine the packed light brown sugar, large eggs, peppermint extract, and vanilla extract. Mix until nicely blended.

Slowly mix the slightly cooled chocolate mixture into the wet ingredients until combined. Gradually add the dry mixture while mixing on low speed, being careful not to overmix.

Cover the bowl with plastic wrap and chill the cookie dough in the refrigerator for about an hour.

Preheat your oven to 325°F (about 163°C) during the last 15 minutes of chilling the dough.

Scoop out about one lightly heaped tablespoon of dough, shape into balls, and place on a baking sheet lined with parchment paper.

Bake the cookies for about 9 minutes. While they bake, cut the marshmallows in half.

After the initial bake, remove cookies from the oven and place one marshmallow half on each cookie, cut side down. Return to the oven for an additional 2-3 minutes until marshmallows start melting.

Press down slightly on the melted marshmallows and let cookies cool on the baking sheet for a few minutes before transferring to a wire rack.

In a medium mixing bowl, sift together the powdered sugar and cocoa powder for the icing.

Heat the remaining butter and half and half in a saucepan over medium heat until melted and simmering. Remove from heat and whisk in the sugar and cocoa mixture until smooth. Add peppermint extract.

Spoon the icing generously over each warm cookie and sprinkle with crushed peppermint candies.