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1
Put oven rack in middle position and preheat oven to 350F.
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2
Line a large baking sheet with nonstick liner.
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3
Grind sugar and zest in a food processor, pulsing 4 or 5 times, until combined well, then transfer to a bowl.
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4
Add butter and vanilla and beat with an electric mixer at medium speed until pale and fluffy, 3 to 5 minutes.
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5
Reduce speed to low, then add egg whites and mix until just combined, about 30 seconds.
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6
Add flour and mix until just combined, about 30 seconds.
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7
Transfer batter to pastry bag and pipe 12 (3-inch-long) lines, about 1 inch apart, on baking sheet.
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8
(Be careful not to squeeze bag too hard lines should only be 1/4 inch wide.)
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9
Bake tuiles until edges begin to brown, 7 to 9 minutes.
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10
Let tuiles stand on baking sheet 20 seconds (just long enough to allow them to firm up slightly), then transfer with offset spatula to rolling pin (stabilized on a cooling rack), draping them diagonally and wiping spatula clean before transferring next cookie.
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11
(If cookies become too crisp to drape, put them back in oven for a few seconds to soften.)
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12
Make more tuiles in same manner, using a cool baking sheet and wiping nonstick liner clean with paper towels between batches.
