Preheat oven to 350º. Mix flour, baking powder and salt in small bowl. Stir bittersweet chocolate and butter in a large saucepan over low heat until melted. Remove from heat. In a medium bowl with an electric mixer, beat eggs, sugar, espresso powder and vanilla, until well blended. Stir egg mixture into chocolate mixture. Stir in dry ingredients. Stir in chocolate chips and nuts.
Drop dough by heaping tablespoons or a ice cream dipper onto a nonstick baking sheet, about 2” apart. Bake until tops crack but cookies are still soft inside, about 10-12 min. Transfer cookie sheet to rack and cool 5 min. Remove cookies to wire rack to finish cooling. Store in an airtight container.