Heat oven to 400 degrees F. Grease and flour* well 12 Madeleine shells.
Beat eggs with salt until frothy; then gradually beat in sugar. Beat the mixture at high speed until very thick and lemon colored, about 15 to 20 minutes.
Fold in the flour, 2 tablespoons at a time, and the lemon peel, if desired.
Add butter, one tablespoon at a time, and fold it in quickly.
Fill shells about 3/4 full and bake for 8 to 10 minutes or until golden.