Combine eggs and sugar in a bowl and mix thoroughly.
Add sifted flour and baking powder, then mix again.
Add melted butter and lemon zest to finish the batter.
Let the batter rest in the refrigerator for about 30 minutes.
Brush the madeleine mold with butter and pour in the batter.
Bake in a preheated oven at 180°C (356°F) for 10-12 minutes.