Preheat the oven to 350° and lightly spray your donut pan with oil. In a medium-size bowl mix together 1 cup of all-purpose flour, 1 tsp of baking powder, 1/4 tsp of cinnamon, 1/4 tsp of nutmeg, and set to the side.
In your Kitchenaid mixer fitted with the paddle attachment, add 1/3 cup of sugar, 1 room temperature egg, and 1 tbsp of melted butter. Mix on high until pale yellow.
Next, add in the 1/4 cup sourdough discard, 2 tbsp of sour cream, 1/2 tsp of vanilla, and 1/4 tsp of salt. Mix until thoroughly combined.
Once combined, add the dry ingredients to the wet and mix until everything comes together. You may need to scrape the sides and the bottom to make sure the dough is thoroughly combined and evenly mixed.
Scoop the sourdough discard donut batter into a quart-size ziplock with one corner cut off and use it as a pastry bag to evenly fill all 6 donut tins with the batter.
Place the pan in the oven and bake for 8-10 minutes or until risen, golden brown, and set in the middle
While the donuts are baking, melt 1 tbsp of butter in a small bowl. In a separate small bowl stir together the 1/8 cup of sugar with the 1/4 tsp of cinnamon.
Once the donuts are finished baking, remove them from the oven and let them cool until you can handle them. Use a small knife to cut out the center to create the donut hole. Brush each donut top with butter and then place them each individually into the cinnamon-sugar mixture until they are covered.
Serve immediately with a cup of coffee and enjoy!