Melt butter or margarine in a saucepan. Add rind, lemon juice, and 1 1/2 cups sugar. Beat eggs and egg yolks until thick, and add to lemon butter mixture. Cook over low heat, stirring constantly until thick. Chill.
Beat 3 egg whites until stiff. Gradually add 1/4 cup sugar, and continue beating until stiff and glossy. Fill baked tart shells with lemon custard, and top with meringue.
Bake at 350 degrees F (175 degrees C) just until tarts are a delicate brown color.
