Combine crumbs, 1/2 cup sugar, and 1/4 cup plus 2 tablespoons butter; stir well. Firmly press crumb mixture evenly in the bottom and up the sides of a 9-inch pie plate. Bake at 350° for 10 to 12 minutes or until lightly browned. Remove from oven. Let cool.
Combine 1 cup sugar, cornstarch, and lime rind in a medium saucepan. gradually add 1 cup whipping cream, stirring until smooth. Add lime juice and 1/4 cup butter; cook over medium heat, stirring constantly, until the butter melts and the mixture thickens and comes to a boil. Remove from heat; let cool. Add sour cream, stirring well. Pour the lime mixture into the prepared crust.
Beat 1 cup whipping cream at high speed of an electric mixer until foamy; gradually add 1/4 cup sugar, beating until soft peaks form. Fold in 3/4 cup sour cream and vanilla. Spread the whipped cream mixture over the filling. Chill at least 4 hours.