Preheat your oven to 350°F (175°C).

In a stand mixer, mix together the all-purpose flour, sugar, baking powder, baking soda, salt, and nutmeg on low speed for 1-2 minutes.

In a separate bowl, whisk together Greek yogurt, milk, eggs, sourdough discard, melted butter, and vanilla extract until smooth.

Pour the wet ingredients into the dry ingredients and gently mix until just incorporated.

Grease your donut pan and fill each cavity about three-quarters full with the batter.

Bake for 14-16 minutes or until golden brown and a toothpick comes out clean.

Let the donuts cool in the pan for 5 minutes, then transfer to a wire rack to cool for an additional 5 minutes.

Place powdered sugar in a sealed bag, add donuts, close, and shake until evenly coated.