Preheet oven to 350 F. In a med bowl, whisk together flour, cocoa, baking powder and salt set aside.
Beat butter and sugar until light and fluffy. Add eggs, one at a time, beating well; mix in vanilla. Combine espresso powder and 4oz melted chocolate; beat into butter mixture. Slowly add flour mixture until combined; fold in chopped 4oz chocolate.
Drop dough by two heaping tablespoons, 3 inches apart, onto two baking sheets. Bake until edges are dry, 14 to 15 minutes, rotating sheets half way through.