Cactus Cookies

From Jenn Johns, Cookies, Cupcakes, and Cardio [1]

Preheat oven to 350°F and grease a baking sheet. Set aside.
In a bowl, mix together your sugar cookie mix, butter, egg, extra flour, and green food coloring until a dough forms. Dust a work surface with extra flour and roll out cookie dough until it is 1/4-inch thick. Cut cactus shapes out of the dough and place on baking sheet.
Bake for 12 to 15 minutes, or until the edges just start to brown and the cookie is cooked through. Remove from the oven and let cool on a wire cookie rack.
Flood cookies with royal frosting and let set. Pipe on decorations and dust with green sanding sugar.