Serves: Makes about 45 cookies
- 1½tablespoons instant espresso powder
- 2 teaspoons warm water
- 1 stick (4 ounces) unsalted butter, softened (65° to 68°F)
- ⅔ cup (4¾ ounces) granulated sugar
- 3 large eggs, at room temperature
- 2¾ cups (13¾ ounces) unbleached all-purpose flour
- ½ teaspoon baking powder
- ¼ teaspoon salt
- 1 cup (4½ ounces) chopped skinned toasted hazelnuts
- 5 ounces good-quality semisweet or bittersweet chocolate, cut into ¼-inch chunks, or 1 cup (6½ ounces) mini chocolate chips
- ½ cup (3½ ounces) superfine sugar
- ½ teaspoon ground cinnamon (optional)
Preheat the oven to 350°F and position an oven rack in the center.
Mix the dough: In the small bowl, stir together the espresso powder and warm water until the powder is dissolved. Set aside.
Place the butter and granulated sugar in the bowl of the stand mixer and beat on medium speed until smooth and slightly lightened in color, 2 to 3 minutes. You can also use a hand mixer and a medium bowl, although you may need to beat the mixture a little longer to achieve the same results. Add the espresso mixture and blend well. Scrape down the bowl with the spatula. Add the eggs, one at a time, beating well (15 to 20 seconds) and scraping down the sides of the bowl after each addition.
In the medium bowl, whisk together the flour, baking powder, and salt. Add to the butter mixture all at once. Turn the mixer to the lowest speed and blend slowly, just until there are no more patches of flour. Turn off the mixer and scrape down the bowl.
Add the hazelnuts and chocolate chips and mix on low just until blended. Remove the bowl from the mixer and stir gently a few times with the spatula to make sure the nuts and chips are evenly distributed and there are no patches of unincorporated flour or butter lurking near the bottom of the bowl.
Shape and bake the dough: Divide the dough in half. On a work surface lightly dusted with flour, gently squeeze and roll each piece to shape into logs about 13 inches long. Line one baking sheet with parchment paper. Place the logs on the sheet about 4 inches apart. Press down on the logs, flattening them slightly until they are each about 2 inches across the top. Place the second baking sheet under the first (to prevent the bottoms of the logs from browning too quickly). Bake for 30 to 35 minutes, until the logs are firm to the touch and lightly golden brown. Transfer the pan to a cooling rack and let the logs cool completely. (If you attempt to slice them while warm, the chocolate will smear and the cookies will look messy.)
Cut the logs and bake them a second time: Turn the oven down to 275°F and position two racks in the top and bottom thirds of the oven. Carefully transfer the cookie logs to a cutting surface. Use the serrated knife to slice the logs on a slight diagonal into cookies ⅛ inch thick. Line the second baking sheet with parchment paper. Place the cookies, cut side down, on the parchment-lined sheets (you'll need both sheets to hold all the cookies). Toast the cookies in the oven, switching the sheets between the racks and rotating each front to back halfway through, for 30 to 40 minutes, until dry and lightly tinged with color. Transfer to a cooling rack.
While the cookies are toasting, prepare the finishing sugar if you like. Whisk together the superfine sugar and cinnamon in the cleaned medium bowl. As soon as the cookies are out of the oven and on the rack, immediately roll them in the cinnamon sugar and return to the baking sheet to cool completely.
Storing: The cookies will keep in an airtight container at room temperature for up to 2 months. If the cookies soften during storage, re-crisp them in a 300°F oven for 10 to 15 minutes, let cool, and return to storage container.