Pour water and tomato juice into a 1 1/2 quart saucepan. Add all but the last 4 ingredients. Stir with a whisk, thoroughly mixing. Bring to a boil, then reduce the heat and simmer for 5 minutes.
Remove bay leaf and stir in lemon juice. Mix cornstarch with 1 tablespoon of water; stir into the sauce. Cook, stirring constantly until the sauce thickens. Whisk in vegetable oil.