Preheat the oven to 350 degrees. Spray your donut pans with baking spray.
With an electric mixer, beat together the butter and sugar until they're light and fluffy. Add the eggs and vanilla and beat until well combined. Add the chocolate and mix to combine.
Sift together the flour, baking soda and salt into a small bowl.
Add half the flour to the chocolate mixer and mix until combined. Add the buttermilk and mix. Then, add the rest of the flour, and mix.
Add ⅔ cup of boiling water and mix.
Fill the donut tins and bake for ten minutes, or until the donuts bounce back when pressed. Cool for five minutes on a wire rack and then unmold. Let cool.
To make the Coconut Glaze: Mix together all the ingredients. With a knife, spread the tops of the donuts with the icing. Sprinkle on the coconut.