Directions:
1. Decide which colours you want to use for decorating, and divide the royal icing into as many bowls. Mix in your food colouring until you've achieved the colours you like.
2. Fill your piping bags with the coloured royal icing.
3. First outline and flood your cookie with the base colour. (See our royal icing tutorials for outlining and flooding for more details.)
4. Once your cookie is flooded, pick a different colour icing, and pipe parallel lines across the surface of the cookie, leaving about 1 cm between each line.
5. Now pick a second colour and pipe another set of parallel lines across the cookie, making sure to pipe them next to the first set of lines.
6. When you've finished piping both sets of lines, set the piping bags aside. Take a toothpick and gently drag the tip through the lines of coloured royal icing. Drag the toothpick through the lines in alternating directions, or all in the same direction for slightly different (but equally pretty) looks.
7. Once you've finished marbling the icing, give your cookie a little shake to smooth everything out, then set it aside to dry for at least one hour. Once dried, store cookies in an airtight container to keep them from drying out. Give as gifts to friends or bring to parties to wow everyone with your decorating skills.
