Put a rack on the lower third of the oven and preheat to 400℉/(200℃).
Generously butter a 12-mold madeleine pan.
Sift together the flour and the baking powder. Set aside.
In a second bowl, in a mixer beat together the egg, granulated sugar, orange zest, and orange blossom water for 30 seconds.
Increase the speed of the mixer to high and beat the mixture until it has quadrupled and is very thick. It should take about 10 minutes.
Using a rubber spatula, carefully fold in the flour mixture and then the melted butter into the egg mixture.
Using a 1 TBSP ice cream scoop, spoon the batter into the prepared molds, filling each about ¾ full.
Bake the madeleines until they are lightly browned around the edges and on the bottom, between 10-12 minutes.
Remove the madeleines from the oven, and immediately flip them out onto a wire rack.
Using a fine mesh sieve or a sifter, dust the orange madeleines with confectioners' sugar.
Best served warm. Makes 12 madeleines.