Clear Orange Filling

1 cup granulated sugar
4 tablespoons cornstarch
1/2 teaspoon salt
1 cup orange juice
2 tablespoons grated orange rind
1 1/2 tablespoons lemon juice
2 tablespoons butter

Mix all ingredients in saucepan. Bring to boil; boil 1 minute, stirring constantly. Chill before using.