Preheat oven to 325°F. In medium bowl, whisk together flour, cocoa powder, baking soda and salt. In a large bowl, whisk together Guinness, egg, granulated sugar and butter. Add dry ingredients to wet ingredients and mix until just combined.
Place batter in ziploc bag and squeeze out air. Cut corner of bag. Spray 6-cup donut pan with non-stick spray. Pipe the batter evenly in the donut pan. It should make 6.
Bake for 15-18 minutes or until stick comes clean. Let cool in pan for 5 minutes and remove and place on cooling rack for 5 to 10 minutes. Dip donuts in glaze.
In small bowl that is wide enough to dip donuts, add powdered sugar, Baileys and water and mix until combined. You may need to add slightly more water to sugar to get right consistency.
Even though they say non-stick, spray your donut pans with non-stick cooking spray to make sure the donuts come out.
Use baking soda that is less than a year old since it has been opened. If you use older baking soda, it won't be powerful enough to help leaven the donuts. You can test it by stirring half a teaspoon of baking soda into a cup of hot water. It will immediately start to fizz and release carbon dioxide gas if it's still fresh enough to use.
When measuring the flour, lightly spoon it into a measuring cup and then level it off with the back of a knife to get the right amount.
You can spoon the batter into the donut pans, but the easiest way to get the batter in the pan is by using a pastry bag or Ziploc bag with the corner cut off.
Just like with any cake type batter that you make, you'll know the donuts are done when a toothpick comes out clean.
Let the donuts cool completely before you dip them in the glaze.
Leftovers will store well in at room temperature for 1-2 days in an air-tight container.