This tutorial will also work with any of the 3 lead Turks Head knots that start with the 5 bight base (3L - 8B, 3L - 11B, etc.) Just follow the same sequence of skip a bight, Over, Under pattern as shown in basic tutorial.
First tie a 3 lead 5 bight Turks Head knot.
Bring second cord Under one, Over one.
Skip one bight and bring cord Over one, Under two (crossing point), Over one.
Skip one bight and bring cord Over two, Under two, Over two.
Skip one bight and bring cord Over two, Under two, Over two.
Skip one bight and bring cord Over two, Under three, over two.
Skip one bight and bring cord Over two, Under three and you are ready to begin doubling the knot.
If you turn the knot inside out you get a very different look.
Doubled
Flattened - two interesting sides.