La Ricetta dei Biscotti al Burro
1 large hard-boiled egg, peeled
3 sticks plus 5 tablespoons unsalted butter, softened
1 cup plus 1 tablespoon confectioners’ sugar, sifted
½ cup plus 1 tablespoon cornstarch
½ teaspoon fine sea salt
3¹⁄³cups cake flour, sifted, plus more for rolling dough
1 large egg
1. Separate the egg yolk and white. Reserve the white for another use and press the yolk through a fine sieve. Set aside.
2. Place the confectioner’s sugar in the bowl of a stand mixer fitted with the paddle attachment. Cream the butter and confectioner’s sugar at high speed (4 or 5 on the mixer) until fluffy and light in color, about 4 minutes.
3. Turn the mixer to low speed and add the egg yolk. Mix for 1 minute. Add the cornstarch and salt and mix to combine. Scrape the sides of the bowl with a spatula, then add the 3¹⁄³ cups flour. Mix on the lowest speed just until combined.
4. Remove the dough, shape into a ball, and wrap in plastic wrap. Refrigerate for at least 2 hours and up to 2 days.
5. Place a piece of parchment paper on the work surface. Place the dough on the paper and sprinkle very lightly with flour. Roll the dough ¼ inch thick. (It may be easier to do this by working with the dough in batches. Keep the remainder refrigerated.)
6. Beat the egg well and brush it on the top of the dough, taking care to wipe the brush clean so that you don’t drip egg down the sides. Slide the parchment paper with the dough onto a cookie sheet or platter and refrigerate for 1 hour.
7. When you are ready to bake the cookies, preheat the oven to 300°F on the convection setting. Use the tines of a fork to press shallow parallel lines into the top of the dough, then turn the tines of the fork at an angle to the first set of lines and make another set of parallel lines to form a diamond grid on the top.
8. Line cookie sheets or sheet pans with parchment and set aside. Use a 2-inch round or oval cookie cutter with a fluted edge to cut out cookies as close to each other as possible to minimize scraps. (Or cut the cookies into squares or diamonds with a sharp knife.) As you cut the cookies, transfer them to the prepared pans.
9. Bake the cookies in the preheated oven until light golden in color, 20 to 25 minutes. Let the cookies cool on the pans on racks, then transfer to a container with some air flow (in other words, not tightly sealed) for longer storage.