Preheat oven to 350 degrees F. Grease a baking sheet or line with parchment paper.
Combine unsweetened chocolate, bittersweet chocolate and butter in top pan of double boiler. When completely melted, continue to cook, adding eggs, sugar, coffee and vanilla extract. Mix well until smooth. Remove from heat.
Sift together flour, baking powder and salt; gradually fold into wet mixture. Fold in chocolate chips and walnuts. Drop large spoonsful onto parchment or greased baking sheet. Bake for 15 to 20 minutes or until dough is firm and set to touch. Remove from sheet and cool on racks.