Preheat the oven to 400°F Lightly grease or spray a non-stick 6 count doughnut pan. Whisk together the dry ingredients in a large bowl. In a small bowl, whisk the sugar, egg, pumpkin, buttermilk and vanilla. Add the wet ingredients to the dry and stir until just combined. Fill the pan three-quarters full in each well. Lightly sprinkle the tops with brown sugar. Bake for 11-12 minutes, until golden and an inserted toothpick comes out dry. Let cool for 5 minutes before turning out onto a cooling rack.
Recipe can easily be doubled. I baked for 12 minutes, but, depending on your stove temp, these might be better cooked for 10 minutes.