What you need:
5 ounces semisweet chocolate
3 ounces unsweetened chocolate
6 tablespoons unsalted butter, at room temperature
1/3 cup all purpose flour
1 teaspoon salt
1 teaspoon baking powder
2 large eggs, at room temperature
2 teaspoons vanilla extract
1 tablespoon instant espresso powder
3/4 cup sugar
3/4 cup semisweet chocolate chips
1/3 cup chopped pecans
1/3 cup chopped walnuts
Preheat oven to 325 degrees
Line several cookie sheets with parchment paper or grease them lightly with butter or vegetable oil.
Melt the 8 ounces of semisweet and unsweetened chocolate and the butter in the top of a double boiler placed over simmering water. Allow it to cool slightly.
Sift the flour, baking powder and salt together into a small bowl and set aside
Using an electric mixer on medium speed, beat the eggs, vanilla, and espresso powder in a medium sized mixing bowl until they are mixed together, about 10 seconds.
Add the sugar to the egg mixture and blend it all until thick, about 1 minute. Scrape the bowl.
Add the melted chocolate and blend 1 minute more. Scrape the bowl.
Add the flour mixture on low speed and mix until blended, 10 seconds.
Fold in the chocolate chips and nuts by hand or with the mixer on low speed.
Drop the dough by generously rounded tablespoonfuls about 2 inches apart onto the prepared cookie sheets, about 20 cookies.
Bake the cookies until they rise slightly and form a thin crust, about 13 minutes.
Immediately remove the cookies from the cookie sheets and place them on a rack to cool.