Position a rack in the center of the oven and preheat to 325 F. Butter a 9 by 5-inch aluminum loaf pan or coat with cooking spray. Dust with flour, tapping out any excess.
Cut the butter into 4 to 5 pieces and add, together with the chocolate, coffee, and espresso powder, to a large heavy bottomed saucepan. Heat over medium-low, stirring frequently with a wooden spoon, until the butter has almost melted, 3 to 5 minutes. Remove the pan from the heat and stir until combined. The mixture will look granular. Set aside to cool to lukewarm, 5 to 10 minutes.
Whisk together the white whole wheat flour, baking soda, and salt in a medium bowl. Lightly beat the egg to blend in a small bowl, and then stir in the Amaretto and vanilla extract. Once the chocolate mixture has cooled, stir in the turbinado sugar and then the egg mixture; stir to combine. The mixture will thicken slightly. Using a large whisk, add the flour mixture in 2 additions, stirring after each addition until just blended; do not overmix. Scrape the dough evenly into the loaf pan.
Bake until a toothpick inserted into the center of the cake comes out with a few moist crumbs attached, about 35 minutes. Place the pan on a wire rack to cool for about 10 minutes. Loosen the cake around the edges with a small sharp knife, unmold, and set it right side up on the wire rack. You can serve the cake warm, or leave it on the rack to cool completely. Just before serving, dust with confectioners’ sugar and slice with a serrated knife.
TO GET A HEAD START: This cake’s deep chocolate flavor improves if baked a few hours or 1 day ahead. Store in an airtight container at room temperature.