Preheat oven to 400F.  Line two 17"x12" baking sheets with parchment.  Fit large pastry bag with a plain 1/2" round tube, or ready a large plastic bag and scissors (make the bag sit up, sides folded down a bit; once you've poured the batter into it, you'll snip off the corner to pipe the batter). 

Sift flour and baking powder together; set aside. 

Place egg whites in a bowl and whip with electric mixer until soft peaks start to form.  Slowly add 2 T (25g) of the sugar and continue to beat until stiff and glossy.

In another bowl, place yolks and stir in remaining sugar.  Whip until thick and very pale in color.  

Fold half the egg whites into the egg yolk mixture.  Fold in the flour, and then fold in the remaining egg whites.

Transfer mixture to pastry bag or plastic bag and pipe out onto prepared baking sheet.  Bake for 8 minutes.