Pour the tequila and the cointreau into a mixing bowl, and with a whisk incorporate other ingredients gradually and slowly until you find the margarita flavor balance you like.  Pour the margarita into a baking pan or other flat bottomed vessel that will fit  a shelf in the freezer (the more surface area, the faster the granita will freeze.)  Using a fork, rake and stir the granita every fifteen minutes until it is completely frozen and evenly crystallized.  Transfer to airtight container and keep frozen until needed.  Keeps frozen for one month.

To serve, open several dozen of your favorite oysters. Using a regular tablespoon (not a measuring spoon) scrap up a spoonful of the granita and add to each raw oyster. Serve quickly.

Serves a couple dozen oysters

More oyster recipes are available from Fred Thompson's book The Big Book of Fish and Shellfish.  This recipe is adapted from the book.