Step 1 Heat the oven to 350 degrees. Place the racks in the upper and lower thirds of the oven. Grease 3 (8-inch) round cake pans, and line the bottom of each with a round of parchment paper.
Step 2 In a large bowl, whisk together the flour, cocoa powder, baking soda and salt.
Step 3In a stand mixer fitted with the paddle attachment, or in a large bowl using a hand mixer, cream together the butter and sugar until light and fluffy, 3 to 5 minutes. Add the eggs, one at a time, mixing until each is incorporated. Add the vanilla and mix to combine. Beginning and ending with the dry ingredients, add the flour mixture and coffee separately, a little at a time, and blending well after each addition.
Step 4Divide the batter among the prepared cake pans and place in the oven. Bake the cake layers until each is puffed and set, and a skewer comes out clean, 30 to 40 minutes, rotating halfway through for even baking.
Step 5Cool the cake layers in their pans on a rack. If not using right away, unmold and cover the cooled cake layers tightly with plastic wrap; the cakes will keep, covered, for one day at room temperature and up to 2 months frozen (thaw before using).
Step 6To make the crumble garnish, trim each cake layer so it is about 3/4-inch thick. Crumble the trimmings onto a parchment-lined rimmed baking sheet and bake for 30 minutes at 350 degrees. Grind the trimmings in a food processor to attain a fine, even crumb. This makes about 6 cups crumble garnish, more than is needed for the remainder of the recipe.