In small bowl, beat eggs slightly. In nonreactive 2-quart saucepan, mix sugar, lemon peel and lemon juice with whisk. Heat to boiling over medium heat. Remove from heat. Quickly stir about 1/2 cup hot mixture into beaten eggs; mix well. Gradually stir egg mixture back into hot mixture. Cook over medium heat, stirring constantly, until mixture just comes to a boil. Gently boil and stir 1 minute. Remove from heat; stir in butter until melted. Let stand 10 minutes.