Add 1 (15.25 ounce) box red velvet cake mix, 2 eggs, and 1/2 cup salted butter to stand mixer bowl, and mix at medium speed until combined.
Use cookie scoop to scoop cookie batter onto parchment paper-lined sheet pan, making sure they are evenly spaces and at least 2 inches apart.
Bake at 350 degrees Fahrenheit for 8-10 minutes, or until cookies are slightly firm. Move cookies from pan to cooling rack and allow to cool completely.
To Make Frosting:
Add 1 (16 ounce) can cream cheese frosting and around 6 drops food coloring to stand mixer bowl, and mix at medium speed until thoroughly combined. Add more food coloring, if needed, for desired color saturation.
To Make Christmas Cookie Sandwiches:
Spread a fully-cooled cookie with around 1-2 tablespoons of frosting, then place another cookie flat-side down onto the frosting to make a cookie sandwich.
Pour around 1/2 cup sanding sugar into a shallow bowl. Roll the edges of the cookie sandwich in the sanding sugar to cover the frosting with sugar.