Sour Cream Lemon Pie

1 cup white sugar
1/2 cup all-purpose flour
or 1/4 cup cornstarch
1/2 teaspoon salt
2 cups milk
1/2 cup sour cream
3 egg yolks
1/4 cup butter or margarine
1 1/2 teaspoons finely shredded lemon peel
1/4 cup lemon juice
whipped cream
1 - 9 inch baked pie shell
                   
1. In a saucepan, combine sugar, flour or cornstarch, and
   salt. Gradually stir in milk. Cook and stir on med heat      
   until thickened and bubbly. Reduce heat, and cook and
   stir 2 more minutes. Remove from heat. 
2. Beat yolks slightly. Gradually stir 1 cup of mix into yolks.
   Return yolk mixture to saucepan, and bring to gentle
   boil. Cook and stir 2 more minutes. Remove from heat,
   and stir in butter, peel, and juice. Fold in sour cream. 
3. Pour filling into baked pie shell, and cool. Top with
   whipped cream.