Break up the semi-sweet chocolate and melt with butter in a double boiler over simmering water or in the microwave on 50% power, stopping to stir every 30 seconds. Let cool for 10 minutes.
In a large bowl, combine the sugars, eggs and vanilla and beat on high speed for 3 minutes. Mix in the melted chocolate on low speed until just blended.
In a medium bowl, whisk together the flour, cocoa powder, baking powder and salt.
Add the flour mixture to the chocolate mixture and mix on low speed until just combined.
Cover and refrigerate for at least 2 hours or overnight. This step is essential for gluten free cookie dough. Do not skip the refrigeration or you will have flat cookies with the potential that they will spread too much during baking.
When you are ready to bake the cookies, preheat the oven to 325 degrees F.
Line two cookie sheets with parchment paper.
Form the cookie dough into rounded tablespoons and space about 2 inches apart on cookie sheets. Flatten with the bottom of a glass into a round disk. I used a glass with a pattern on the bottom to create the pattern on the cookie wafer.
Bake on the middle rack for 12 minutes.
While the cookies are baking, cut 12 marshmallows in half and crumble the candy canes into fine pieces. I broke up the candy canes by putting time into a plastic bag and smashing them with the back of an ice cream scooper.
Let the cookies cool for 2 – 3 minutes – just cool enough that you can move them without them falling apart.
Flip over half the cookie wafers and top with one-half marshmallow and sprinkle with candy cane crumbles.
Top the cookies with the other wafers and return to the oven for 2 – 3 minutes, until the marshmallows melt. Remove from the oven and center the wafers while the marshmallows are still soft.
Let cool until the marshmallows set. Once the marshmallows set, but before the marshmallows are no longer tacky (3 – 5 minutes), roll in the crushed peppermint.