1. Sift flour into a mixing bowl, and set aside.

2. In the bowl of an electric mixer fitted with the paddle attachment, beat butter and sugar on medium speed, until well-combined, about 2 minutes. Beat in egg whites, one at a time, beating for 4 minutes after each addition. Add the reserved flour, and mix until just combined.

3. Reserve 1/2 cup batter; place in a pastry bag fitted with a #2 tip, and set aside for piping chocolate tuile cookies.