In a mixing bowl combine powdered sugar, butter, dry drink mix and the egg. Mix until smooth.
Stir in flour, salt and cream of tartar.
divide dough into 8 equal pieces. Roll each piece into a ball and roll each ball in the orange sugar until coated, pressing into dough if needed. Chill balls for 20 minutes.
Preheat oven to 350 degrees F. Line a baking sheet with parchment paper.
Slice each ball into 8 wedges. Place wedges on lined baking sheet, fitting 24-28 wedges on a sheet. Bake for 8-10 minutes. Cool cookies completely.
Melt dipping chocolate in a glass bowl for 1 minute in the microwave. Add additional time in 15 second increments until smooth and melted. (Do not overheat!)
Dip half of each cookie in chocolate and cool on parchment paper. Store in an airtight container.