1) Combine everything except the liquor in a bowl, beating until smooth.
2) Chill the mixture in the refrigerator until it's very cold, overnight if possible. Make sure the canister for your ice cream maker is in the freezer, too; at least 24 hours is preferable.
3) Pour the base into your ice cream maker canister, and freeze according to manufacturer's directions.
4) Transfer the sherbet from the canister to a freezer-safe container. If desired, stir in the liquor of your choice; this will keep the sherbet from becoming rock-hard in the freezer.
5) Freeze until firm, about 4 hours. If you haven't used liquor to keep it soft, remove the sherbet from the freezer about 15 to 20 minutes before you want to serve it, to soften.
Yield: about 1 quart sherbet.