Preheat oven to 450 degrees. Spray 2 (6 count) doughnut pans with cooking spray.
In a mixing bowl, whisk together the flour, cocoa powder, baking powder, baking soda and salt. In another mixing bowl, whisk together the sugar, eggs, oil, milk, and vanilla. Add the wet ingredients to the dry ingredients and whisk to combine. Spoon the batter into the doughnut pans, filling each form about ¾ full. Bake for 7 – 9 minutes or until the doughnuts spring back when lightly touched and a tooth pick inserted into a doughnut comes out clean. Let cool in the pan for 2 -3 minutes then remove to a baking rack to finish cooling completely. Can be made a day or two ahead.
In a small saucepan melt the peanut butter, powdered sugar, and 5 tablespoons milk over medium heat, stirring until smooth. Add more milk if needed to make a glaze-like consistency. Dip the doughnuts into the glaze and sprinkle with chopped peanuts.