1. Preheat the oven to 350°F (175°C) and lightly grease a six-cavity donut pan

2. Whisk together flour baking powder cinnamon nutmeg and salt in a medium bowl

3. In a separate bowl whisk sourdough discard melted butter sugar egg and milk until smooth

4. Pour the wet mixture into the dry ingredients and stir until just combined without overmixing

5. Transfer batter to a piping bag or spoon and fill each donut cavity two thirds full

6. Bake for 10 to 12 minutes until tops spring back lightly and edges are pale golden

7. Allow donuts to cool in the pan for 5 minutes then transfer to a cooling rack

8. Stir sugar and cinnamon together in a small bowl and melt butter in another dish

9. Brush each warm donut with melted butter and roll in cinnamon sugar until coated

10. Serve immediately or store in an airtight container at room temperature