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1
Preheat the oven to 350 degrees F.
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2
In a heavy skillet, melt the butter over medium heat.
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3
After it melts, continue to cook the butter, watching carefully.
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4
It will foam and subside, and then separate into golden butterfat and cloudy white milk solids.
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5
The milk solids will begin to brown.
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6
When they are lightly browned and the butter smells nutty and toasted, remove from the heat and set aside to cool.
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7
In a mixer fitted with a whisk attachment (or using a hand mixer), whip the egg whites and sugar until stiff and glossy.
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8
Add the flour, vanilla, and brown butter and mix at low speed until blended.
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9
The batter will become thicker as the egg whites lose volume.
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10
Using an offset spatula, an icing spatula, or the back of a spoon, spread the batter in circles to form thin disks on silicone baking mat-lined baking sheets.
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11
(You may only fit 6 or 8 per pan.)
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12
The batter should be so thin that you can see the pan through it.
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13
Bake until light golden brown, 8 to 10 minutes.
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14
When the cookies come out of the oven, immediately lift them off the sheet pan with your fingers or a spatula and roll them up on a wooden spoon handle; then slide them off.
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15
Repeat with the remaining batter.
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16
The batter will probably start to stiffen up as the butter cools; you can reheat it in the microwave, or set the bowl over hot water to keep the batter warm.
