Have all ingredients at room temperature, about 70°F. Preheat the oven to 325°F.
Mix together into a paste in a small bowl:
Use this mixture to grease two 9 × 5-inch loaf pans or one 9- or 10-inch tube pan. Whisk together in a medium bowl:
Set aside. Have ready:
Beat in a large bowl, or in a stand mixer with the paddle attachment, until creamy:
Gradually add and beat until light and fluffy, 5 to 7 minutes:
Beat in:
Beat in the melted chocolate until combined. Beat in one at a time until combined, scraping down the sides of the bowl frequently:
Gently mix in the flour mixture in 3 parts, alternating with:
in 2 parts. Mix just until combined. Scrape the batter into the prepared pan(s). Bake until a toothpick inserted in the center comes out clean, about 1 hour for the loaf pans, about 15 minutes longer for the tube pan.
Let loaves cool in the pans on a rack for 10 minutes; a tube pan for 15 minutes. Turn the cake(s) out of the pan(s). Turn loaves right side up to cool. Let a tube cake cool upside down.