Step 1Place a rack in the center of the oven and heat the oven to 300 degrees. Line a baking sheet with a silicone mat. Or line with foil, dull side facing up, and smooth the foil to remove any wrinkles (to avoid distorting the cookies). Lightly butter the mat or foil.
Step 2In a small bowl, combine one-eighth teaspoon of the salt and pepper. Set aside.
Step 3In a large bowl, whisk together the butter, sugar, egg whites, flours and the remaining one-eighth teaspoon salt. The batter will have the consistency of thin, runny Cream of Wheat cereal.
Step 4If using a silicone mat: Drop level teaspoons of batter 2 inches apart onto the baking sheet. If you intend to shape the tuile, bake only four or five at a time to allow time for shaping. Using a small offset spatula, spread the batter into rounds, ovals or elongated shapes about one-sixteenth-inch thick. Sprinkle a pinch of the salt and pepper over each. Bake, watching carefully, until the wafers are golden brown one-half to three-quarters of the way to the centers, but still pale in the centers, 10 to 15 minutes. If the cookies are not baked long enough, they will not be completely crisp when cool. As soon as you can coax a thin metal spatula under a cookie without destroying it, transfer it to a rack to cool flat. Or shape it by draping it over a rolling pin, nestling it into a little cup or twisting it with your fingers. Working fast, remove the remaining tuiles; reheat for a few seconds if necessary. Repeat until all of the wafers are baked.
Step 5If using foil: Drop level teaspoons of batter 2 inches apart onto the baking sheet. If you intend to shape the tuile, bake only four or five at a time to allow time for shaping. Sprinkle a pinch of salt and pepper mixture over each. Bake, watching carefully, until the batter spreads and the cookies are golden brown one-half to three-quarters the way to the centers but still look pale in the center, 10 to 15 minutes. If the cookies are not baked long enough, they will not be completely crisp when cool. If the cookies do not spread thin while baking, try using a little more butter on the foil and/or spread the batter with an offset spatula or the back of a spoon. For flat tuiles, slide the foil sheet of cookies onto a rack to cool. For curved tuiles, grasp the edges of the foil when the sheet comes out of the oven (without touching the pan or the cookies) and roll it into a fat cylinder, gently curving the attached cookies like potato chips. Crimp or secure the foil with a paper clip. When cool, unroll the foil carefully and remove the tuiles. Alternatively, remove individual tuiles from the foil while they are hot and shape them as described above. Flat or curved, tuiles are easiest to remove from the foil when completely cool. Repeat until all the wafers are baked.