These cookies are made with lots of butter, some sugar, and a sourdough starter discard. The method of mixing the ingredients by hand allows for consistently flat and smooth cookie tops!
Mix the gluten-free flour, xanthan gum, and salt in a medium-sized mixing bowl and set aside.
In a large mixing bowl, add softened butter, sugar, egg, sourdough starter discard, vanilla, and the flour mix. Bring the dough together with your hands. I don't recommend using an electric mixer to avoid incorporating air into the dough.
Turn the dough onto a well-floured working surface. If the dough is too sticky, roll it in flour on all sides to make it easier to work with.
Roll out the dough with a rolling pin into a large square or a rectangular. The thickness should be about ¼ in or ½ cm.
Take a long offset spatula and slide it under the dough to make sure it isn't sticking to the surface. Then, cut out the shapes with the cookie cutters.
Line your baking sheet with parchment paper or a silicone baking mat and transfer the unbaked cookies to it. You don't need to leave much space in between the cookies as they aren't going to spread.
Bake for 9-11 minutes at 350F/175C or until the edges just barely start browning. Let the cookies chill for a minute or two and transfer them to the cookie tray.
Make the Icing
Add 675g of powdered sugar and 3 egg whites to a large mixing bowl and mix using an electric mixer until it looks thick and smooth (2-3 minutes).
Depending on how many different colors you will need, separate the icing into a few separate bowls. Add a different food coloring to each one of the bowls. Make sure not to use a liquid food coloring or the icing will become too soft.
Take each color and separate them into 2 different bowls, one will be thicker for outlining the cookies, and the other one will be more liquid to fill in the outline.
Add 1 teaspoon of cold water to one of the bowls of the same color.
Use the thicker icing to outline the pattern on the cookies and use the thinner one to fill in the space within the outline. Use a toothpick to help spread the inner filling to reach the outline.
Notes
Make sure to use room-temperature ingredients for the best results. Caster sugar is finer than granulated sugar but not as fine as powdered sugar. I recommend using either caster or powdered sugar in these cookies. Wait until the cookies cool down completely before decorating them. Store the cookies in the fridge for up to a week.
Nutrition
Serving: 1cookie without the icingCalories: 92kcalCarbohydrates: 15.4gProtein: 1.1gFat: 3.2gSaturated Fat: 1.8gCholesterol: 20mgSodium: 437mgPotassium: 23mgFiber: 2.9gSugar: 3.8gCalcium: 6mg