Generously butter a madeleine pan. Then, dust it lightly with flour, tapping out any excess. This step is crucial to ensure your madeleines release easily after baking. You can also use a baking spray that contains flour.

In a mixing bowl, whisk together the eggs and sugar until the mixture is pale and slightly thickened. This usually takes about 2-3 minutes. You’ll notice the mixture becomes lighter in color and a bit more voluminous.

Stir in the vanilla extract and lemon zest (if using) into the egg mixture. The lemon zest adds a beautiful fragrance and bright flavor to the madeleines, but you can skip it if you prefer.

In a separate bowl, whisk together the flour and salt. Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Be careful not to overmix; a few lumps are okay.

Slowly pour in the melted and cooled butter, gently folding it into the batter until everything is well combined. The batter should be smooth and slightly glossy.

Cover the bowl with plastic wrap and refrigerate the batter for at least 30 minutes, or up to 2 hours. Chilling the batter helps to prevent the madeleines from spreading too much during baking and gives them their signature hump.

Preheat your oven to 375°F (190°C). Spoon the batter into the prepared madeleine pan, filling each shell about three-quarters full.

Bake for 11-13 minutes, or until the edges are golden brown and the madeleines spring back lightly when touched. Keep a close eye on them, as baking times can vary depending on your oven.

Let the madeleines cool in the pan for a few minutes before gently removing them to a wire rack to cool completely. Dust with powdered sugar before serving, if desired.