This is my recipe for making traditional royal icing, used for cookie decorating and cake decorating. It uses raw egg whites and dries hard!Traditional Royal Icing uses raw egg white and lemon juice. It's generally considered safe, but is best avoided for pregnant people, small children, and immunocompromized people.
In clean stand mixer, whip egg whites until foamy.
Add lemon juice, whip for another minute.
Slowly add powdered sugar until cookie icing reaches desired consistency. You will want a fairly thick frosting – but still smooth and workable – for piping details and borders.
If you're not using it immediately, transfer to an airtight container, cover surface with plastic wrap, and secure lid tightly.
Re-whip before use.
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Notes
See post for full details on how to use this frosting, including the different consistencies you can mix it to, and their uses.