Ensure your mixing bowl and whisk or mixer attachments are completely clean and free of any grease or oil. If unsure, wipe them with a little vinegar and dry thoroughly. Any fat can prevent the egg whites from whipping properly and will make the icing too thin and dull.

Add the egg whites (or pasteurized liquid egg whites) to the mixing bowl. Using a stand mixer with the whisk attachment or a hand mixer, beat on medium speed until the egg whites are foamy and light, about 1–2 minutes. You are aiming for frothy, not stiff peaks.

Mix in the vanilla extract, almond extract (if using), lemon juice (if using), and a pinch of fine sea salt. Beat briefly until evenly combined so the flavor is distributed throughout the icing.

Turn the mixer to low speed. Add the sifted powdered sugar about 1/2 cup at a time, letting each addition fully incorporate before adding more. This keeps the icing smooth and helps avoid a cloud of sugar in your kitchen.

Once all of the powdered sugar has been added, increase the mixer speed to medium-high. Beat for 3–5 minutes, scraping down the sides and bottom of the bowl once or twice, until the icing is thick, glossy, and holds soft peaks. For stiff piping consistency (outlines and details), the icing should hold a peak that only slightly bends at the tip. If it looks dull or grainy, beat a bit longer. If it is very stiff and chunky, add water 1 teaspoon at a time until smooth.

Adjust the icing to the consistency you need: leave it thick for stiff piping and gingerbread house “glue,” thin slightly for medium consistency (borders and simple designs), or thin further for flood icing to fill and smooth over cookies. To thin, add water 1/2 teaspoon at a time, mixing well after each addition, until you reach about a 10–15 second consistency for flooding (a line drawn through the icing disappears in 10–15 seconds). To thicken, sift in additional powdered sugar 1–2 tablespoons at a time until the icing holds its shape.

Divide the icing into separate bowls for each color. Add gel food coloring a little at a time with a toothpick or a small squeeze, stirring gently until the color is uniform. Go slowly—colors deepen as they sit. For deep shades like red or black, make the icing ahead of time to allow the color to intensify so you can use less coloring. Leave some icing white if desired.

Royal icing crusts quickly when exposed to air. Whenever you are not actively using it, press plastic wrap directly onto the surface of the icing in the bowl and then cover the bowl with a lid or towel. For piping bags, tuck the tips into a damp paper towel or cover with plastic wrap to keep the icing from drying out.

Let the mixed and colored icing rest for about 15 minutes to allow air bubbles to rise to the surface and for colors to deepen slightly. Gently stir and tap the bowl on the counter to release bubbles before transferring the icing to piping bags or squeeze bottles for decorating.