Cool Lime Pie

From limes, finely grate 4 teaspoons peel and squeeze 2/3 cup juice. In large bowl, with wire whisk, stir undiluted condensed milk, lime peel, and lime juice until blended. Whisk ice cream into condensed-milk mixture until evenly blended (mixture will be the consistency of sour cream). Pour ice-cream mixture into piecrust. Freeze at least 6 hours or until firm. If not serving pie same day, wrap and freeze up to 1 week. To serve, uncover pie and let stand at room temperature 10 minutes to soften slightly for easier slicing. Meanwhile, in small bowl, with mixer at medium speed, beat cream until stiff peaks form. Top each serving of pie with a dollop of whipped cream and sprinkle with lime-peel slivers.