Preheat the oven to 325 degrees F. Butter 2 madeleine pans (with 12 molds each) using 2 tablespoons of the melted butter, and set the pans aside.
Combine the eggs, sugar, and salt in a medium-sized mixing bowl. Place the bowl over a pot of gently simmering water and stir constantly. Once the ingredients are warmed through and the sugar has dissolved, remove the bowl from the heat. Using an electric mixer, beat the mixture until it is pale yellow, light, and slightly thickened. Fold in the sifted flour, remaining butter, and lemon zest.
Use a small spoon to drop a generous tablespoonful of batter into each mold of the prepared pans. Bake until the batter is set like a cake and golden brown, about 12 to 15 minutes. Release the madeleines from the pans and cool on a parchment paper lined cooling rack.
Yield: 24 cookies