This makes about 1 to 6 servings, depending on who is eating it:
Heat the oven to 350 degrees.
Mix flour, sugar and salt.
Whisk in butter, grated rind, and egg yolks and blend until smooth. Whisk in lemon juice and milk.
Beat egg whites until stiff and fold into the lemon mixture.
Butter a 1 1/2 quart pyrex or ceramic casserole. Place casserole in a pan of hot water and bake for one hour. Chill.