Slice lemons, with rind still on, as thinly as possible, preferably paper thin; place in a bowl. Add 2 cups sugar and let stand, stirring occasionally, until sugar is well absorbed, at least 2 hours, but overnight is best.
Roll out pastry to line pie plate. Beat eggs well; add nutmeg, if using. Arrange layers of lemon slices and their juice over the unbaked pastry, sprinkling each with extra sugar as you go. Pour egg mixture over all.
Roll out remaining pastry and place over filling crimping edges. Cut vents in center. Paint crust with milk and sprinkle with sugar. Bake at 450F for 10 minutes. Reduce heat and to 350F and bake 35 minutes more, or until a knife inserted in the center comes out clean. Chill before serving.