Preheat oven to 350 degrees F (175 degrees C). Grease cookie sheets or line them with parchment paper. In the top of a double boiler, melt together the unsweetened chocolate, 1 cup of the chocolate chips and the butter. This can also be done in a microwave oven on low setting. Stir occasionally until melted. In a medium bowl, beat the eggs and sugar until thick and light, about 3 minutes. Stir in the espresso. Add the chocolate mixture, mix well. Sift together the flour and baking powder, fold into the egg mixture. Carefully fold in the chopped nuts and remaining chocolate chips. Drop dough by tablespoonfuls 2 inches apart onto the prepared cookie sheets. Bake for 10 to 12 minutes in the preheated oven. Cookies will have a crackled appearance when done. Cool on baking sheets.