1. Preheat oven to 350°. Whisk together condensed milk and next 3 ingredients until well blended. Pour mixture into piecrust.
2. Bake at 350° for 15 minutes or until pie is set. Cool completely on a wire rack (about 1 hour). Chill 1 hour before serving.
3. Beat whipping cream at high speed with an electric mixer 2 to 3 minutes or until soft peaks form, gradually adding powdered sugar. Top pie with whipped cream. Garnish, if desired.
*Regular lime zest and slices may be substituted.
Note: We tested with Nellie & Joe's Famous Key West Lime Juice.