Michael e-mailed the Kitchen Shrink with this question. He said that he wanted to make clear dessert sauces and had heard that cornstarch or arrowroot was the answer but he had never used either.
Cornstarch and arrowroot are similar ingredients to work with. Both have almost twice the thickening power of flour. Cornstarch, which is inexpensive and a staple in most home pantries, produces a clear, shiny sauce while arrowroot, a more expensive ingredient found in the spice section of the supermarket, produces an even clearer sauce. To thicken a sauce with either cornstarch or arrowroot, whisk the starch into a cool or room temperature liquid and then into the sauce. Don’t allow the sauce to cook too long after thickening or the starch will lose some thickening power.