Preheat the oven to 300°.
In a large mixing bowl of an electric mixer, beat the butter on medium speed for 30 seconds.
Add the powdered sugar, cocoa, and peppermint extract, mixing until well combined.
Slowly add in the flour until just blended, then add ¾ cup chocolate chips.
On a cookie sheet covered with parchment paper, pat the dough into a 9" circle.
Using a fork, prick the dough deeply to form 16 pie shaped pieces.
Bake at 300° for 25 minutes or until the edges are firm and the center is set.
Cool on cookie sheet for 2 minutes.
With a long, sharp knife, cut shortbread into wedges along the perforations. Transfer wedges to a wire rack.
Melt the remaining ½ cup of chocolate chips in a microwave at 30 second intervals until completely smooth.
Using a knife, gently spread the chocolate over the tops of the shortbread pieces. Sprinkle with the sparkling sugar.