PREPARE and bake single pie crust according to recipe directions, using a 9-inch pie plate; cool.
WHISK together sugar, milk, egg yolks, lemon juice, corn starch and lemon peel in a medium, heavy saucepan. Heat over medium heat, stirring until mixture becomes thick. Remove from heat. Stir in butter. Cool at room temperature. When filling is cool, stir in sour cream.
POUR filling into baked pie crust, smoothing top evenly. Refrigerate at least 4 hours before serving. Garnish with whipped cream and lemon peel strips, if desired.