1/4 cup butter, softened
1 1/2 cups confectioners' sugar
2 1/2 tablespoons cream of tartar
1/2 teaspoon lemon juice
1/4 teaspoon vanilla extract
2 egg whites
2 tablespoons lemon juice
In a medium saucepan, combine butter, sugar, cream of tartar and lemon juice. Bring to a boil, stirring constantly. Boil, stirring occasionally, until mixture reaches desired consistency. Remove from heat and chill in refrigerator.
Pour mixture into a small bowl, and chill until completely chilled. Pour mixture onto a serving plate. Separate 1/2 cup lemon filling and lemon rind. Apply mixture to filling and lemon rind in remaining 1/2 cup lemon juice. Chill until no longer than 2 hours.