Beat eggs with sugar until pale yellow. Add zest.
Whisk together dry ingredients then add to the egg mixture gently, until just combined. Add melted butter.
Refrigerate the batter at least 1 hour or overnight, necessary for traditional "hump".
Use pastry brush to lightly grease a non-stick Madeleine pan. Put the pans in the freezer until needed.
Spoon 1 Tbsp of batter into the center of the well. It will spread out by itself.
Bake 7-8 minutes at 350F until slightly golden around edges and centers look set and slight hump has appeared. Allow to cool slightly and remove from the tin and allow to cool.
Once cooled completely and dust with powdered sugar and serve!