In 3-quart saucepan, heat whipping cream just to boiling over low heat. In small bowl, beat egg yolks, sugar and 1 teaspoon orange peel with fork or wire whisk until well blended. Stir small amount of hot cream into yolk mixture, then stir yolk mixture back into cream in saucepan. Cook over low heat 10 to 15 minutes, stirring constantly, until mixture coats a spoon. DO NOT BOIL. Remove from heat. Cool 30 minutes or until room temperature. Stir in liqueur. Refrigerate until serving.