Preheat oven to 350. In a large bowl, cream butter.
Add sugar, flour salt, lemon juice and rind.
In a separate bowl, beat egg yolks; stir in milk. Slowly add second mixture to first mixture.
Beat egg whites until stiff; gently fold into mixture.
Pour into ramekins or individual souffle dishes and place in pan of hot water. Bake in "moderate" oven (350, in my case) for 45 minutes. You will have a layer of lemon custard, with gorgeous, lightly browned sponge on top. Let cool a bit.
Turn out and serve with whipped cream, or serve still in the dish.