In a bowl, combine the flour, baking powder, and salt. Set aside.
In another bowl, beat the eggs, sugar, and lemon zest with an electric mixer for about 5 minutes or until the mixture forms a ribbon when the beater is lifted.
With a whisk, gently fold in the dry ingredients. Fold the butter in the same way. Cover and refrigerate for at least 30 minutes.
With the rack in the middle position, preheat the oven to 200 °C (400 °F). Butter and flour a small madeleine pan. Set aside.
Fill each cavity three-quarter up with batter. Bake for 8 to 10 minutes or until the madelienes are lightly golden brown. Remove from the pan and let cool completely on a wire rack. Repeat with the remaining of the batter. If desired, serve with lemon curd.
This batter will keep for three to four days in the refrigerator. Madeleines are best baked the same day they will be eaten. The baking time for standard-sized madeleines is about 14 minutes.