Preheat the oven to 350 degrees. Grease two (8½ × 4½ × 2½-inch) loaf pans, line the bottoms with parchment paper, then grease and flour the pans.
Pour the boiling water into a 2-cup glass measuring cup, add the bitter-sweet chocolate, cocoa powder, and coffee granules, and stir until the chocolate melts. Set aside to cool for at least 15 minutes.
In a medium bowl, sift together the 2 cups flour, the baking powder, and salt and set aside. In another bowl, combine the walnuts, chocolate chips, and the 2 tablespoons flour and set aside.
In the bowl of an electric mixer fitted with the paddle attachment, beat the butter, granulated sugar, and brown sugar together on medium speed for 2 minutes. With the mixer on low, add the eggs, one at a time, and then the vanilla, scraping down the bowl with a rubber spatula. Alternately in thirds, add the flour mixture and the chocolate mixture, beginning and ending with the flour. Fold in the nut mixture with a rubber spatula.
Divide the batter equally between the prepared pans, smooth the tops, and bake for 45 to 55 minutes, until a toothpick inserted in the middle comes out clean. (Test in a few places because you might hit a warm chocolate chip.) Cool in the pans for 30 minutes, turn out on a cooling rack, rounded side up, and allow to cool to room temperature.
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