Moosewood Restaurant Book of Desserts - an excellent book that I highly recommend - and it is a winner every time. I usually like to make this as a layer cake, with two layers and icing in between, but this time I made it in a bundt pan.
1 1/2 cups boiling water
3/4 cup unsweetened cocoa powder
2 cups flour
1 1/4 tsp baking soda
1/8 tsp salt
1 cup butter at room temperature
1 1/3 cups packed brown sugar
2 large eggs
2 tsp vanilla extract
coffee icing ingredients
1/2 cup butter, at room temperature
3 1/2 cups icing sugar
4 Tbsp strong coffee
In a mixing bowl, add a bit of the boiling water to the cocoa, making a paste, and then whisk in the rest of the water. Set aside.
Preheat oven to 350 F. Butter and flour the cake pan(s).
Sift together the flour, baking soda, and salt and set aside. In another bowl, cream the butter and brown sugar. Add the eggs one a time, beating well after each addition. Mix in the vanilla extract. Add the flour mixture alternately with the cooled cocoa mixture, beating after each addition.
If using two cake pans, divide batter evenly (or just pour into the bundt pan). Bake for 25-30 minutes for two cakes (40-45 minutes for bundt), until a knife inserted into the centre comes out clean. Cool the cakes in the pans for 10 minutes and then turn them out onto racks to cool completely.
For the icing, cream the butter and icing sugar. Gradually add the coffee until the icing is a good consistency for spreading. You may need more/less sugar or coffee and you can just keep on adding until it's right. If you want, you can grate a little dark chocolate over the cake. Enjoy!