1 1/2 cups sugar
2 tablespoons instant espresso powder
1 tablespoon vanilla extract
2 cups fine-quality bittersweet (56 percent to 60 percent cacao) chips or 1/4-inch chunks
2 cups coarsely chopped walnuts (about 8 ounces)
POSITION the oven racks in the center and upper third of the oven and heat the oven to 325°. Line 4 large baking sheets with parchment paper.
MELT the semisweet chocolate and butter in a large, heavy-bottomed saucepan over medium-low heat until smooth, 5 to 7 minutes, stirring occasionally.
WHISK together in a medium bowl the flour, baking powder and salt.
BEAT together in the bowl of a stand mixer fitted with the paddle attachment, or in a large bowl using a hand mixer, the eggs, sugar, espresso powder and vanilla until blended and slightly foamy, 1 to 2 minutes. Beat in the melted chocolate mixture, then the flour mixture. Stir in the bittersweet chocolate and walnuts.
USING 3 tablespoons of dough for each cookie, spoon the dough onto two of the prepared baking sheets, forming about 6 cookies per sheet. Bake until the cookies are cracked on top and moist in the center, about 14 minutes (do not overbake so as to keep the center of the cookies moist and fudgy). Transfer the baking sheets to a rack and cool the cookies completely before removing. Remove the cookies gently using a metal spatula.
Nutrition information: Per cookie: 347 calories, 5 grams protein, 33 grams carbohydrates, 2 grams fiber, 23 grams fat, 11 grams saturated fat, 45 milligrams cholesterol, 25 grams sugar, 73 milligrams sodium.