I didn't have the three 6-inch cake pans Benjamina used to create the cake pictured in her book (above). But you all know I have an endless collection of bundt pans. So that's what I used. I baked the batter in a single 9-inch / 8 cup quantity bundt pan. My sense is you can get away with baking in a single 13x9 pan, or two 8-inch rounds as well (adjusting the timing, of course). A long way of saying, don't be deterred if you don't have the "correct" pan. Bake until a cake tester or toothpick comes out clean. That said, if you have an oven that runs hot, keep an eye on things. It's better to underbake this cake a shade rather than over bake - because of the whole grain aspect its more likely to end up dry.
Preheat the oven to 350°F / 180°C with a rack in the center. Butter and flour a 9-inch / 8-cup bundt pan, or equivalent*. See head note.
Sift together the flour, sugar, cocoa powder, baking powder, baking soda, and salt in a large bowl. In a medium bowl whisk together the eggs, milk, and vanilla extract. Mix in the melted butter. Pour the wet mixture over the dry ingredients and stir until uniform. Add the coffee and stir until the batter is smooth. Pour the batter into your prepared pan and bake for 45-50 minutes, or until a cake tester comes out clean. Leave the cake to rest for ten minutes, and turn out onto a rack to cool completely.
Whisk together the powdered sugar, salt, vanilla extract, and tahini. Add 2 tablespoons of the buttermilk, and stir until smooth and thick. Add another tablespoon, or so, if needed to get the icing to a consistency you like - not so thick that it won’t spread down the cake, or so thin it runs right off. Somewhere between.
Makes 1 9-inch cake.