Preheat the oven to 350°F (175 °C). Prepare a six-donut pan by greasing it with Pam or some vegetable oil. Place on a rimmed baking sheet and set aside for later.
In a small bowl, whisk together the flour, baking soda, salt, and pinch of nutmeg. Set the dry ingredients aside.
In a medium bowl, whisk together the sour cream, granulated sugar, vegetable oil, vanilla extract, and the egg. Switch to a spatula and stir in the dry ingredients.
Fill a pastry bag (without a tip) with the batter and pipe it evenly among the prepared doughnut pans. The batter should reach about half way up the inside of each doughnut pan.
Bake the doughnuts for 12–16 minutes until the top edges begin to turn golden brown.
Remove the rimmed baking sheet from the oven and let the doughnuts cool for about 5 minutes before tossing them in the extra granulated sugar.