Preheat the oven to 350 degrees.

Prepare a 12 x 18 x 1-inch baking sheet with butter and flour or line a baking sheet with parchment paper or foil and spray with cooking spray.

Melt together the butter, 1 pound of chocolate chips, and the unsweetened chocolate in a medium heatproof bowl over a pan of simmering water or use a double boiler instead. Do not let the water boil, you do not want to burn the chocolate.

Allow the mixture to cool slightly. In a large bowl, combine eggs, coffee granules or espresso, vanilla, and sugar, stir until combined(do not beat).

Stir the warm chocolate mixture into the egg mixture and allow too cool to room temperature. Make sure the chocolate is warm, not hot, you do not want to make scrambled eggs.

In a medium bowl, sift together 1 cup flour, the baking powder, and salt. Add to the cooled chocolate mixture to the dry ingredients.

Toss the walnuts and 12 ounces of chocolate chips in a separate bowl with 1/4 cup of flour, then add them to the chocolate batter. Pour the brownie batter into the baking sheet.

Bake for 20 minutes, then rap the baking pan against the oven shelf to force the air to escape from between the pan and the brownie dough. Bake for another 12-15 minutes, until a toothpick comes out clean. Do not overbake the brownies, they will dry out.

Allow the brownies to cool thoroughly in the half sheet pan, refrigerate, and then cut into 20 large squares of 40 smaller squares.