Preheat the oven to 400°. Spray your donut tins with cooking spray or brush with a neutral oil.
Mix the flour, sugar, baking powder, and salt in a large bowl. Set that aside.
In another bowl, mix peanut butter, egg, milk, coconut oil, and vanilla.
Pour the wet ingredients into the dry ingredients and mix until just combined. Do not overmix. Fill the donut pans with the batter. I find the easiest way to do this is by piping the batter into the pan, but you could just as easily spoon it into the pan. The batter will fill 12 donut pans.
Bake for 18-20 minutes depending on your oven. The donuts should be lightly browned.
Top the donuts with icing, or roll in cinnamon and sugar. Enjoy immediately.