Instructions

1. Sift the powdered sugar into a medium bowl to remove any lumps. This helps prevent clogged piping tips and gives a smooth finish.
2. Add 3 tablespoons milk or water, the corn syrup, vanilla, almond extract if using, and a pinch of salt. Stir gently with a spatula or whisk until thick, smooth, and glossy, about 30 to 60 seconds.
3. Adjust thickness a few drops of liquid at a time until a ribbon of icing disappears into the surface in 15 to 20 seconds for outlining. For flooding, thin a portion to an 8 to 10 second ribbon. Stir slowly to avoid air bubbles.
4. If using lemon juice, stir it in now. Taste and adjust flavors; add a touch more vanilla or almond if desired.
5. Divide icing among small bowls and tint with gel food coloring. Add color gradually with a toothpick, stirring until evenly blended. Let colors rest 5 minutes to develop.
6. Transfer outline icing to piping bags fitted with small round tips (sizes 1 to 3 work well) or snip a very small opening in a zip-top bag. Pipe outlines on cooled cookies and let set 2 to 3 minutes.
7. Thin icing for flooding if needed, then transfer to squeeze bottles or piping bags. Flood inside the outlines and use a toothpick or scribe tool to nudge icing to the edges and pop any bubbles.
8. Let base layers dry at room temperature until the surface is set, 6 to 8 hours. Add details with thicker icing, then dry fully 12 to 24 hours before stacking or packaging.