Geode Cookies

Preheat oven to 350° and line two large baking sheets with parchment paper.

Roll small 1” balls out of sugar cookie dough and place them about 1 1/2” apart on the prepared baking sheets.
Using your hands, press down on the cookie dough balls to make them look a bit misshapen. (You want them to look like rocks!)
Bake for 12 minutes. Let cool completely before decorating.

Make the icing: In a small bowl, whisk together powdered sugar and 2 tablespoons milk.
If the icing is too thick, gradually add a bit more milk.

Roll the edges of the cooled cookies in icing, then roll the edges in colorful sanding sugar, alternating colors.
Let set until the icing has hardened, about 15 minutes.

Working one cookie at a time, spoon more icing onto the center of each cookie.
Drop a tiny bit of food coloring onto the icing then use a toothpick to swirl the food coloring to create an agate look.
Sprinkle with white sanding sugar and more colorful sanding sugar, then decorate the cookie with rock candies.
Let set completely before serving.