In a large mixing bowl, combine the sifted powdered sugar and egg whites.
Using an electric mixer, beat the mixture on low speed until it becomes combined, about 1 minute.
Increase the mixer speed to medium and continue to beat for about 4-5 minutes, or until the mixture forms stiff peaks.
Add lemon juice and vanilla extract (if using) into the mixture, then mix on low speed for another minute until fully incorporated.
If you want to color your icing, divide the mixture into smaller bowls and add a drop or two of food coloring to each bowl, mixing until you achieve the desired color.
Cover the bowl with a damp cloth or plastic wrap to prevent the icing from drying out until ready to use.
Notes
Transfer the royal icing into piping bags with various sized tips for easy decorating.
Keyword cookie decoration, easy recipe, royal icing