Place the Thai black rice and 3 cups of water in a medium saucepan and simmer over a medium-low heat, stirring constantly. Simmer 2 hours (stirring occasionally) or until the rice has completely dissolved into the water. You should have a liquid the consistency of creamy potato soup.
Add 1/2 of the roasted garlic to the black rice, and simmer 5 minutes more. Pass through a fine mesh strainer.
While the Thai black rice is cooking, place the basmati rice and 3 cups of water in a medium saucepot and repeat all the steps you followed to cook the black rice juk. In addition to the garlic, add the horseradish to the basmati juk before passing through mesh strainer. The basmati juk should take 30 minutes less in total cooking time.