Cut the pomegranates in half. Place a fine mesh sieve over a large bowl. Using a spoon or your fingers, scrape the seeds into the sieve.

With a wooden spoon or a flat meat pounder, press on the seeds to extract 2 cups of juice. Discard the seeds and set the juice aside.

In a medium saucepan, mix the cornstarch with the sugar. Slowly stir in the pomegranate juice and mix well. Cook the sauce over medium heat, stirring constantly, until the sauce begins to thicken and darkens to a deep wine color, and the sauce coats the back of the spoon. Remove from the heat and let cool. The sauce may be made ahead and stored in a jar in the refrigerator. It will thicken somewhat if stored. When ready to use, thin with a little warm water if necessary.