For crust, in a medium bowl, combine graham-cracker crumbs and the 2 tablespoons sugar. Add the 1/3 cup melted butter and toss to mix well. Spread mixture evenly into a 9-inch pie plate, pressing onto bottom and up side to form a firm, even crust. Bake in a 350 degree F oven for 6 minutes or until edge is lightly browned. Cool on a wire rack.
Meanwhile, for filling, in a medium saucepan, combine the 1 cup sugar, the cornstarch, milk, and egg yolks. Cook and stir over medium-high heat until the mixture is thickened and bubbly. Reduce heat. Cook for 2 minutes more. Remove from heat.
Gently stir in lemon juice, the 1/4 cup cut-up butter, and the lemon peel. Add sour cream, mixing gently until just combined. Pour filling into crust. Cover and chill in the refrigerator for at least 4 hours or up to 6 hours.
To serve, in a chilled bowl, combine whipping cream, the 4 teaspoons sugar, and the vanilla. Beat with chilled beaters of an electric mixer on medium speed until soft peaks form (tips curl). Top pie with dollops of the whipped cream. Garnish with lemon twists, if you like. Store leftover pie in the refrigerator. Makes 8 servings.