Ingredients:
2 cups chocolate porter or stout beer
8 tablespoons unsalted butter, plus more for the pan
3/4 cup natural cocoa powder (non-dutched)
1 cup / 5 oz whole wheat flour
1 cup / 4.5 oz all-purpose flour
1 cup / 4.25 oz muscovado or dark brown sugar
1 1/2 teaspoons baking soda
3/4 teaspoon fine grain sea salt
3 large eggs
1 1/2 cups plain whole yogurt
3/4 cup pure maple syrup
Chocolate Buttermilk Icing:
3/4 cup / 2.75 oz powdered sugar
1/4 cup natural cocoa powder (non-dutched)
2 tablespoons buttermilk
Directions:
Preheat oven to 350F / 180C, with a rack in the center.
Butter and flour (generously) a 11 or 12-cup capacity bundt pan (or equivalent).
In a saucepan simmer the beer down to 1 cup / 240 ml. Remove from heat, add the butter and stir until melted. Stir in the cocoa powder, mixing until smooth, then set aside to cool, stirring occasionally to let off heat.
In a medium bowl, whisk together the flours, sugar, baking soda, and salt. Set aside.
In a large mixing bowl, combine the eggs, yogurt, and maple syrup. Whisk well, until nicely blended and uniform in appearance. Gradually add the (cooled) stout mixture, stirring all the while. Stir until well blended. Add the flour mixture, folding until just blended, using as few strokes as possible.
Transfer the batter to the prepared pan and bake for 35 - 45 minutes if using the bundt pan, or until a knife inserted in the center comes out clean. You really don't want to over bake this cake - err on the slightly moist side if anything. Remove from the oven, and turn out onto a cooling rack after seven minutes.
In the meantime, make the icing by whisking together the powdered sugar, cocoa, and buttermilk. The icing should end up smooth and creamy looking, adjust with a touch of powdered sugar or a few extra drops of buttermilk if you want to tweak the consistency at all. When the cake is completely cool, run the icing around the top with an offset spatula and let it set.