Melt the butter and let it cool slightly.
Rub the sugar with the lemon zest between your fingers until the sugar is fragrant and slightly moist.
Add the eggs and the pinch of salt and beat for a few minutes until light, creamy, and fluffy.
Stir in the vanilla.
Mix the flour with the baking powder and gently fold in.
Add the melted, lukewarm butter and fold in until you have a smooth batter.
Cover the batter and chill for at least 1 hour (better 2-3 hours or overnight). This is key for the signature hump.
Preheat the oven to 200 °C (400 °F) top/bottom heat. Grease and lightly flour the madeleine tin.
Depending on your tin, add 1-2 teaspoons of cold batter into each mold (fill only about ¾, don’t spread it - the batter settles on its own).
Bake for about 10-12 minutes, until the edges are golden and the hump has formed.
Let cool briefly, then remove from the tin and let cool on a wire rack.
