Sift the sugar. Add powdered sugar to a bowl and sift to remove lumps. This small step makes a big difference in smooth icing.

Add the liquids. Stir in 2 tablespoons of milk, corn syrup, vanilla, and a pinch of salt. Whisk until the mixture looks thick and glossy.

Adjust consistency. For outline consistency, you want a slow ribbon that holds its shape. For flood consistency, add milk a few drops at a time until the icing smooths out within 10–15 seconds after you drizzle it back into the bowl.

Divide and color. Split the icing into small bowls. Add gel food coloring a little at a time, stirring thoroughly. Keep each bowl covered with plastic wrap touching the surface to prevent crusting.

Bag the icing. Use piping bags fitted with small round tips or snip a tiny hole in disposable bags. For flooding, a squeeze bottle works well for control.

Outline the cookies. Pipe a thin border around each cookie. Let it set for 2–3 minutes so it acts like a dam and keeps flood icing in place.

Flood the center. Fill the outlined area with flood-consistency icing. Use a toothpick or scribe tool to nudge the icing into corners and pop any bubbles.

Add details. For wet-on-wet designs (like hearts or dots that settle in), add them immediately while the flooded base is still wet. For crisp details, wait 20–30 minutes for the base to crust over.

Dry properly. Let cookies dry at room temperature, uncovered, for at least 6–8 hours, or overnight for fully set icing. Avoid humidity and direct heat.

Store or serve. Once dry, the icing will be firm to the touch but not rock hard. Cookies can be stacked with parchment between layers.