Tangerine Filling

 1 cup sugar

4 tablespoons cornstarch

1/2 teaspoon salt

1 cup tangerine juice

2 tablespoons tangerine zest

1 1/2 tablespoons lemon juice

2 tablespoons butter or margarine

Combine all the ingredients in a large saucepan. Bring to a boil over high heat; boil for 1 minute, stirring constantly. Chill before using.