In a large bowl, cream butter. Mix in sugar, flour, lemon juice and lemon zest. Beat in egg yolks, then milk.
In a large glass or metal mixing bowl, beat egg whites until stiff peaks form. Gently fold into the lemon mixture. Pour filling into pie crust. Scatter blueberries evenly over the top.
Bake in the preheated oven for approximately 50 minutes, or until filling is set. Cover the pie with foil after about 30 minutes to avoid browning. Allow to cool slightly before serving.