In a small bowl whisk together the flour, baking powder, and salt.
In the bowl of your electric mixer, or with a hand mixer, beat the eggs and sugars at high speed until the mixture is thick and pale in colour (about 5-8 minutes).
Beat in the vanilla extract and orange zest.
Add the flour mixture over the whipped eggs and gently fold in, using a rubber spatula or whisk (do not over mix or the batter will deflate).
Then take about 1 cup (240 ml) of the batter and fold it into the warm melted butter (this lightens the butter making it easier to fold into the batter). Then, with a spatula, gently fold the butter mixture completely into the egg batter.
Cover and refrigerate the batter for at least two hours, preferably overnight (can be stored in the refrigerator for up to three days).
Preheat your oven to 190 degrees Celcius.
Using a pastry brush, generously grease the moulds of two Madeleine pans (preferably non stick) with very soft or melted butter. Then dust the moulds with flour, tapping out the excess flour.
Refrigerate the pans until the butter hardens (about 10 minutes). Make sure the pans are well greased or the Madeleines will stick and be hard to remove.
Drop a generous tablespoonful (can use an ice cream scoop) of the batter into the centre of each prepared mould, leaving the batter mounded in the centre. This will result in the classic "humped or domed" appearance of the Madeleines.
Bake the Madeleines for about 10 minutes, until the edges are golden brown and the centres spring back when lightly touched. Do not overbake these cookies to prevent them from becoming too dry.
Remove the pans from the oven and tap each pan against the counter to release the Madeleines immediately.
Place Madeleines on a wire rack to cool. Best served immediately but can be stored in an airtight container at room temperature for a couple of days or frozen for up to 1 month.
Dust with powdered sugar before serving.