Mix sugar, cornstarch and salt in saucepan. Stir water in gradually. Bring to boil over direct heat, stirring constantly. Boil 1 minute. Remove from heat. Stir in butter and lemon rind. Add lemon juice in gradually. Cool thoroughly.
Rich Lemon Filling: Follow above recipe, but after the mixture has boiled 1 minute, stir half of hot mixture into 2 slightly beaten egg yolks. Blend into remaining mixture. Boil 1 minute more. Remove from heat and add the butter, lemon rind and lemon juice.
Clear Orange Filling: Follow basic method, but use: 1 cup sugar, 1/4 cup cornstarch, 1/2 teaspoon salt, 1 cup orange juice, 2 tablespoons butter, 2 tablespoons grated orange rind, and 2 tablespoons lemon juice.
Pineapple Filling: Follow basic method, but use: 1/2 cup sugar, 3 tablespoons cornstarch, 1/2 teaspoon salt, 3/4 cup pineapple juice, 1 cup well-drained crushed pineapple, 1 tablespoon butter, 1 teaspoon lemon juice. Cool thoroughly.