Wash and cut 2 of the lemons into paper-thin slices. It is very important to slice the lemons as thinly as possible; use a very sharp knife or an electric meat slicer, if on is available. Remove peel and pith of remaining lemons; slice the flesh very, very thinly, and put it with the other slices in a large mixing bowl. Add sugar, and toss well to coat. Cover bowl with plastic wrap, and let the mixture rest overnight, stirring occasionally.
The next day, preheat oven to 450 degrees. Press one circle of pastry into an 11-inch pie plate and chill.
Add beaten eggs to the lemon mixture, and mix well. Turn mixture into prepared pie shell, neatly arranging some of the lemon slices on top. Cut long, even slashes 1 inch apart in the other pastry round, and place on top of filling. Crimp edges of the pie to seal. Brush top and edges with egg-white glaze. Bake for 15 minutes. Reduce oven temperature to 375 degrees and continue baking for 30 minutes, or until the crust is golden brown and shiny. Let cool on a rack before serving.
Makes a 10" pie. 3 lemons, 3 cups sugar, 7 eggs, 1 egg white, 1/8 tsp salt