Once you have baked and cooled your cookies, lay them out on your work surface. I like to decorate on baking sheets, or on laid-out parchment paper.

Use a stiff or medium consistency icing to pipe a border around the entire cookie, as well as any internal separation lines you may want.

Use royal icing that has been thinned to flow consistency to flood icing throughout the appropriate sections.

Repeat with other colors, as necessary.

Allow the cookies to dry overnight, until the base layer of icing is hard.

Use a stiff or medium consistency royal icing to pipe your details over the flooded and dried cookies.

Allow fully decorated cookies to fully dry - at least another 24 hours - before packaging or storing in an airtight container.