Preheat the oven to 350° F. Prepare a standard doughnut pan by lightly spraying with baking spray.
In a large bowl, whisk together the flour, sugar, cocoa powder, baking powder, coffee, and salt. In a small bowl, whisk together the buttermilk, oil, eggs, and vanilla. Gently stir in the buttermilk mixture into the flour mixture, until just combined.
Fill the doughnut pan about 2/3 full – I use a pastry bag to make this easier, but it is not necessary. Bake for about 12-15 minutes or until a toothpick inserted into the doughnuts come out clean. Let the doughnuts cool for a few minutes before gently remove the doughnuts from the pan.
Make the glaze by brewing the coffee in the boiling water for 5 minutes. Strain into a bowl, and stir in vanilla and salt. Whisk in the powdered sugar in 1/2 cup increments until smooth and you achieve your desired consistency, using a little more or less as necessary. Dip the doughnuts in the glaze and let the excess drip off. Let it cool on a wire rack…or enjoy immediately.