Melt the butter over low heat, but don’t burn it. Leave it to cool.
Place the 2 whole eggs, the yolk and the sugar in a bowl and whisk them until they are blanched.
Sift in the flour and baking powder and mix to form a smooth dough.
Add the vanilla powder, stir it in, then incorporate the melted butter. Mix again.
Put it in a piping bag, seal it and refrigerate for at least 2 hours (or even overnight).
Alternatively, cover the bowl with plastic wrap. Make sure you preheat the oven to 180°C 15 minutes before baking.
Take the mix out of the refrigerator just before you are ready to bake it. It’s the thermal shock of the cold mix in the hot oven that gives the madeleines their famous curved shape.
Snip the tip off the piping bag and fill the molds three-quarters full.
Bake for 10/13 minutes, keeping an eye on them to make sure they don’t brown too much.
Turn out the madeleines and let them cool completely on a wire rack.