Heat oven to 400°F. Combine 1/3 cup sugar and 1/2 cup butter in large bowl. Beat at medium speed, scraping bowl often, until creamy. Reduce speed to low; add flour, 1 tablespoon lime peel, milk and vanilla. Beat until well mixed. Press onto bottom and up sides of greased 10-inch tart or quiche pan. Bake for 15 to 20 minutes or until light golden brown. Cool completely.
Meanwhile, combine 1 cup sugar, lime juice and 1 tablespoon lime peel in 2-quart saucepan. Cook over medium heat until sugar is dissolved (1 to 2 minutes). Reduce heat to low.
Beat eggs and egg yolks in small bowl with wire whisk. Stir small amount of hot sugar mixture into egg mixture using wire whisk. Gradually stir egg mixture into hot sugar mixture. Continue cooking, stirring constantly, until mixture is thickened (6 to 8 minutes).
Remove from heat. Stir in 6 tablespoons butter, 1 tablespoon at a time, with wire whisk. Cool 15 minutes.
Pour cooled filling into crust; smooth top. Cover; refrigerate at least 2 hours.
Just before serving, beat whipping cream in small bowl at high speed, scraping bowl often, until stiff peaks form (2 to 3 minutes). Place whipped cream in pastry bag fitted with large star tip. Pipe whipped cream onto tart; sprinkle with 2 teaspoons lime peel. *Substitute regular lime peel and lime juice. TIP: To get the most juice from limes, grate limes first. Then microwave limes on HIGH for 30 to 45 seconds to warm slightly before juicing. If additional Key lime juice is needed, add bottled Key lime juice.