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Foolproof Royal Icing That Hardens Perfectly for Stackable Sugar Cookies

Close-up of sugar cookies topped with piped, pastel rainbow sugar cookie icing that hardens.
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Learn how to make sugar cookie icing that hardens completely, dries smooth, and achieves a professional, glossy finish. This easy recipe is perfect for decorating holiday cookies that you can stack and gift.

Ingredients

Scale
  • 2 cups powdered sugar, sifted
  • 3 tablespoons meringue powder
  • 1/4 teaspoon cream of tartar
  • 6 tablespoons warm water
  • 1 teaspoon clear vanilla extract (optional, for whiter icing)
  • Gel food coloring (optional)

Instructions

  1. In a medium bowl, whisk together the sifted powdered sugar, meringue powder, and cream of tartar until fully combined.
  2. Add the warm water and clear vanilla extract (if using) to the dry ingredients.
  3. Beat the mixture with an electric mixer on low speed until the ingredients are incorporated, then increase the speed to medium-high.
  4. Beat for 5 to 7 minutes until the icing is very smooth, bright white, and holds stiff peaks. This process incorporates air, which helps it dry hard.
  5. Check the consistency. For outlining, the icing should be thick. For flooding (filling in areas), add water one teaspoon at a time until the icing flows smoothly but still holds a line on the surface for a few seconds.
  6. Separate the icing into bowls if you plan to color it. Add gel food coloring sparingly and mix until the color is uniform.
  7. Use the icing immediately for outlining cookies. Let the outline dry for 15 to 30 minutes before flooding the center.
  8. To flood, use a spoon or a piping bag with a larger tip to fill the outlined area. Gently shake the cookie to settle the icing into a smooth layer.
  9. Allow the cookies to dry completely at room temperature, away from humidity. This can take 6 to 24 hours depending on the thickness and humidity. The icing is ready when it is hard to the touch and no longer tacky.

Notes

  • For the whitest icing, use clear vanilla extract instead of standard brown vanilla extract.
  • If your icing seems too thick after resting, stir in a few drops of water. If it is too thin, mix in a tablespoon of powdered sugar.
  • Humidity is the enemy of royal icing. Decorate on dry days if possible, or use a dehumidifier in your decorating space.
  • Once dry, store decorated cookies in an airtight container at room temperature. They are stackable once fully hardened.

Nutrition

Find it online: https://tastetaught.com/sugar-cookie-icing-that-hardens/