Preheat oven to 350°F.
Use approximately 1 Tablespoon of the melted butter to brush the inside of six, 8-ounce ramekins; set aside. (Let the remaining butter cool slightly.)
In a large bowl, beat together butter, egg yolks, lemon juice and lemon zest. In a small bowl, combine sugar, flour and salt: add alternately with the milk to the egg mixture.
In a separate large bowl, beat egg whites until firm peaks form. Fold egg whites into lemon mixture.
Pour batter into the prepared ramekins and set the ramekins in a large baking dish. Pour hot water into the baking dish to a level about halfway up the side of the ramekins. Bake for 25-30 minutes or until tops are golden brown. Serve the cakes warm or chilled. Garnish with berries or a dusting of powdered sugar.
2 medium lemons are needed for zest and juice.