Melt butter and add lemon zests. Gently beat eggs and sugar and incorporate the sifted flour and baking powder. Add the warm butter with zests, cover and refrigerate overnight (12 hours) before baking.
Use extra soften butter to grease nonstick madeleine baking pan. Pipe out 30g portions.
Set the oven rack adjusted to the middle position with a baking sheet or a pizza stone. Bake one cookie sheet at a time (12 madeleines).
Bake in a preheated 500ºF/260ºC oven for 5 minutes, then lower to 350ºF/180ºC and continue baking for 7 minutes more.
Lower temperature to 25ºF/15ºC if using a convection oven. Enjoy!