Hard Cookie Frosting

Place the egg whites in a clean, dry bowl. Beat with a mixer on medium-high speed until stiff peaks form. Add the powdered sugar, cream of tartar, extract, and desired coloring and beat until all is incorporated and smooth. Adjust the color as needed while mixing.

Frost cookies and let dry at room temperature until hardened. Store in an airtight container once the frosting is set.

cook's notes

This recipe contains egg whites. You can substitute dried egg whites (which are pasteurized) or meringue powder if you wish (results won't quite be the same though). Use 2 teaspoons of meringue powder or dried egg whites with 2 tablespoons of warm water for each egg white called for. Stir until dissolved and let cool to room temperature before using. Different brands may call for different amounts of water to reconstitute, always follow your package directions if they differ.

You can also use liquid food coloring but it doesn't work as well as paste if you want vibrant colors.