In a large bowl, whisk together gluten-free flour blend, xanthan gum, cocoa powder, baking soda, and salt. Set aside.
Cream together butter and sugar with a hand mixer until light and fluffy.
Add in eggs and peppermint extract and mix until combined.
Add in dry ingredients, a little bit at a time, and mix until just combined. Stir in 3/4 cups of the chocolate chips.
Refrigerate dough for at least an hour before baking.
When ready to bake, preheat oven to 350F. Line two baking sheets with parchment paper.
Scoop out the dough into 18 balls and place on the baking sheet, leaving at least 2 inches between each ball.
Bake at 350F for 10-12 minutes, until edges are set. Remove from the oven and allow to cool for 5 minutes on the pan before placing on a cooling rack.
As soon as the cookies come out of the oven, place half of a marshmallow on top of each cookie.
To melt the chocolate, add the remaining half cup of chocolate chips to a microwave safe bowl. Microwave in 30 second increments, stirring in between, until chocolate is melted. It typically takes about 1-2 minutes total.
Drizzle chocolate over the cookies with a spoon or a pastry bag. Sprinkle with crushed candy canes. Allow chocolate to set completely before serving.