Preheat oven to 350 degrees F. Grease six 6-oz custard cups.
Zest the lemons and measure out 1 tablespoon of zest.
Juice the lemons and measure out 1/3 cup of juice.
In a small mixing bowl using a handheld electric mixer, beat the egg whites and salt util soft peaks form. Gradually sprinkle in 1/2 cup sugar, beating until whites are stiff and sugar has dissolved.
In a large bowl, using the electric mixer at medium, beat the egg yolks and remaining 1/4 cup of sugar until blended. Add the lemon zest, lemon juice, milk, flour and melted butter. Beat scraping sides of bowl with a rubber spatula.
With a heavy duty scraper, fold beaten egg whites into yolk mixture.
Carefully pour the batter into the greased custard cups (or ramekins).
Set the cups in a 13x9 inch baking pan. Place on oven rack and pour boiling water (I used very hot water from the tap) into the pan so that it comes halfway up sides of custard cups. Bake for 40 to 45 minutes until tops are golden brown and firm.
Let cool on a wire rack.