Preheat Oven, Grease Pan:

Set oven to 400°F (205°C). Coat a 12-cavity donut pan thoroughly with non-stick cooking spray.

Whisk Dry Ingredients:

In a large bowl, combine flour, sugar, baking powder, cinnamon, nutmeg, and salt with a whisk.

Mix Wet Ingredients:

In another bowl, whisk together buttermilk, eggs, and oil.

Combine Wet and Dry:

Pour wet mixture into dry mixture and stir gently until just combined; avoid overmixing.

Fill Donut Cavities:

Transfer batter to a piping bag and fill each cavity to about half to two-thirds full.

Bake Donuts:

Bake for 7–9 minutes, until tops are lightly golden and they spring back when pressed.

Cool and Coat with Sugar:

Let cool in pan for 5 minutes, then move to a wire rack. While still warm, coat donuts in powdered sugar.