Preheat oven to 350℉. Grease a standard donut tin. Set aside.
In a medium bowl, whisk together the flour, sugar, baking powder, salt and nutmeg. Set aside.
In a large bowl, whisk together the buttermilk, eggs, melted butter and vanilla.
Add dry ingredients to wet ingredients, then mix to combine (avoid over-mixing).
Using a piping bag or a spoon, transfer the batter to the prepared donut tin, filling each cavity about three-quarters full. Bake donuts at 350℉ for 10 minutes or until a toothpick inserted into one comes out with little to no crumbs. Allow the donuts to cool in the pan for a couple minutes before inverting them onto a wire rack.
Place powdered sugar into a ziplock bag. One at a time, place a warm donut in the bag and gently shake to coat the donut. Remove and repeat with remaining donuts. If the sugar isn’t sticking, brush melted butter on the donut and shake in the bag again.
Notes
Cornstarch will help prevent the powdered sugar from dissolving on the donuts. Whisk 2 teaspoons cornstarch with 1 cup powdered sugar.Nutmeg is optional, but recommended to create that classic cake flavor.Store donuts in an airtight container at room temperature for 5 days.