Lemon Tart

In saucepan, combine sugar and cornstarch. Slowly add milk. Cook and stir till thickened. Reduce the heat and cook another 2 minutes. Remove from the heat and stir in a little of the hot liquid into the yolks and then return it all to the pan. Bring to a gentle boil, stirring constantly and cook another 2 minutes. The mixture will be very thick. Remove from heat and stir i butter and lemon peel. Gentle stir in lemon juice. Let cool completely, covered. Fold in sour cream, pour into pie shell. Refrigerate at least 2 hrs before cutting. You can garnish with whipped topping.