Preheat oven to 350 degrees F. and grease 2 large heavy baking sheets. In a double boiler or a metal bowl set over a saucepan of barely simmering water melt unsweetened chocolate, 1 cup chocolate chips, and butter, stirring until smooth, and remove top of double boiler or bowl from heat. In a bowl with an electric mixer beat eggs, sugar, and ground coffee on high speed until very thick and pale and mixture forms a ribbon when beaters are lifted, about 3 minutes, and beat in chocolate mixture. Into mixture sift in flour, baking powder, and salt and stir until just combined. Stir in remaining chocolate chips and walnuts.