Step 1

In a med saucepan ,mix together the sugar and cornstarch, then add the milk.Bring mixture to a boil and cook for 3-4 minutes. Mix a small amount with beaten yolks to temper, then stir back into pan.Stir in the lemon juice, lemon extract, salt and butter. Cook until thickened, maybe another minute.Remove from heat and cool for about 5 minutes, then stir in the sour cream.

Step 2

Pour into prebaked pie crust. If desired serve with whipped cream!