Meanwhile, in small bowl combine eggs, egg yolk and sugar; mix until smooth. In small saucepan, bring lime juice to a boil; stir into egg mixture. Return to saucepan and heat, whisking constantly 3 minutes or until mixture is pale yellow and coats the back of a spoon. Remove from heat; add butter, vanilla and salt. Cool in the refrigerator at least 1 hour. Once cooled, fold whipped topping into mixture.