Heat oven to 350°F. Mix flour, baking powder and salt in small bowl.
Melt half of semisweet chocolate, the unsweetened chocolate and butter in top of double boiler; stir until smooth.
Beat sugar, eggs and espresso on high speed in bowl until ribbonny, 3 minutes. Fold in melted chocolate. Stir in flour mixture. Fold in remaining chocolate pieces.
Drop batter, 1 tablespoon per cookie, 2 inches apart, on greased baking sheets.
Bake in 350°F oven 12 minutes, until puffed and crackly. Cool slightly on sheets. Transfer to racks to cool.
