6 tablespoons all purpose flour
1/4 teaspoon baking powder
1/4 teaspoon salt
8 ounces bittersweet (not unsweetened) or semisweet chocolate, chopped
1/2 cup (1 stick) unsalted butter
2 large eggs
3/4 cup sugar
2 1/4 teaspoons instant espresso powder
2 1/4 teaspoons vanilla extract
1 cup semisweet chocolate chips
1 cup coarsely chopped walnuts.
Preheat oven to 350°F. Mix flour, baking powder and salt in small bowl. Stir bittersweet chocolate and butter in heavy large saucepan over low heat until melted. Remove from heat.
Using electric mixer, beat eggs, sugar, espresso powder and vanilla in medium bowl until well blended. Stir egg mixture into warm chocolate mixture. Stir in dry ingredients. Stir in chocolate chips and chopped walnuts.
Immediately drop dough by heaping tablespoonfuls onto nonstick baking sheets, spacing 1 1/2 inches apart. Bake until tops crack but cookies are still soft inside, about 12 minutes. Transfer baking sheets to racks; cool 5 minutes. Transfer cookies to racks; cool completely. (Can be prepared 1 day ahead. Store cookies in airtight container at room temperature.)