In a medium size microwave-safe bowl or a 2 cup Pyrex measure, melt the butter on high for about 30 seconds. Add the chopped unsweetened chocolate and semisweet chocolate. Stir well and microwave at 50% power, stirring every 30 seconds, until melted. Set aside to cool slightly

In a mixing bowl using an electric mixer, beat the eggs with the sugar for about 4 minutes or until light and fluffy and slightly thick. Add espresso powder, vanilla extract and chocolate mixture, beating until smooth.

In a small bowl mix together flour, baking powder, and salt and add to chocolate mixture, beating until just combined. Stir in the nuts. Chill for about 20 minute or just long enough to cool down the mixture (only if it is warm). When mixture is no longer warm, stir in the chocolate chips or chunks. If mixture is still soft, return to the refrigerator until it is scoopable.

Preheat oven to 325 degrees F. Scoop dough into 12 equal size mounds and arrange the mounds on a foil lined plate. Keep chilled until ready to use (or put them in a zipper bag, freeze them and bake as needed), or arrange 3 ½ inches apart on ungreased baking sheets. Bake one sheet at a time for 20-25 minutes on center rack (check sooner if you made the cookies smaller).

Bake cookies in batches in middle of oven 25 minutes, or until tops begin to crack (do not overbake). Cool cookies on a rack.