Preheat the oven to 350 degrees F (175 degrees C).
In a large bowl, stir together the flour and sugar until well blended. Stir in butter until smooth. Gradually beat in the egg yolks, lemon juice and milk. In a clean glass or metal bowl, whip egg whites with an electric mixer until stiff but flexible peaks form. Fold egg whites into the lemon mixture. Transfer to a casserole dish.
Bake for 35 minutes in the preheated oven, or until set. Serve warm or chilled.