While they look unassuming, these ultra-tender cookies are superbly flavorful. Appearing here courtesy of YouTube pastry chef star Claire Saffitz and her first cookbook, Dessert Person, Claire notes the cookies feature “two of the best nuggets of baking knowledge” she’s ever acquired: making the dough with sieved hard-boiled egg yolk and “toasted” flour. These two unusual ingredients yield a cookie that’s absolutely irresistible.
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Preheat the oven to 425°F with a rack in the center position.
To toast the flours: In a medium bowl, whisk the flours together and spread them across a large, rimmed baking sheet (a half sheet pan works well here).
Bake the flours, stirring once after about 5 minutes, until they've browned and smell toasty, 8 to 12 minutes. They'll smoke a little while baking; that’s OK.
Remove the baking sheet from the oven, turn the oven off, and let the flours cool completely.
To make the dough: Sift the cooled flours, salt, and baking powder through a fine-mesh sieve set over a medium bowl.
Place the egg yolks in the sieve and use the back of a spoon to press them through the mesh into the flour mixture. Stir to combine, then set aside.
In a separate large bowl, give the butter a few strokes with a flexible spatula to make sure it’s smooth and spreadable.
Add the granulated sugar and vanilla and beat vigorously with the spatula until the mixture is light and creamy, about 1 minute.
Fold in the flour mixture and stir to make a soft, well-blended dough.
Scrape the dough onto a sheet of plastic wrap and pat it with your dampened hands into a 7" to 8” square. Wrap tightly in the plastic and refrigerate until firm, about 1 hour (or up to 3 days).
Toward the end of the chilling time, preheat the oven to 350°F.
To prepare the cookies: Remove the dough from the refrigerator, unwrap it, and let it soften for 5 minutes or so.
Place the dough between two sheets of parchment and roll it about 3/8” thick and approximately 8 1/2" x 9” in size.
Brush the surface of the dough with a thin layer of the beaten egg. Sprinkle generously with the demerara sugar.
Using a knife, pastry cutter, or pizza wheel, cut the dough into 1” to 1 1/2" diamonds or rectangles.
Leaving the cookies in place on the parchment (don't separate them), slide both parchment and cookies onto a baking sheet.
To bake the cookies: Bake the cookies until they’ve puffed and the edges are browned, 18 to 22 minutes.
Remove the cookies from the oven; leave the oven on.
Cut the cookies again (retracing the lines you made earlier), but don't separate them just yet.
Allow the cookies to cool on the pan until you’re comfortable handling them.
Position one rack in the top third of the oven and one rack in the bottom third. Line a second baking sheet with parchment paper.
Separate the cookies and place half on the second baking sheet, spacing them evenly apart.
Bake both pans of cookies until they’re evenly browned all over, 10 to 12 minutes, switching racks and rotating the pans after 6 minutes. The cookies will seem soft when they come out of the oven but will crisp as they cool.
Let the cookies cool completely on the baking sheets.
Store cookies airtight at room temperature for up to five days; freeze for longer storage.
