Preheat the oven to 425 degrees F and spray your muffin pan with a non-stick oil.
Next, warm the butter and milk in a small saucepan until the butter is melted, and allow it to cool for a few minutes.
Then, add the mixture to a mixing bowl and stir in the oil, applesauce, sour cream or Greek yogurt, egg, sourdough discard, vanilla extract, and sugar until combined.
To the same bowl add the flour, baking powder, baking soda, salt, and nutmeg.
Then, divide the batter among the prepared muffin pan using a 1.5 tablespoon cookie scoop or measuring spoons.
Bake the donut muffins at 425°F (220°C) for 3–4 minutes, then reduce the oven to 350°F (175°C) and continue baking for 8–10 minutes, or until a toothpick comes out clean.
Remove the muffins from the oven and allow them to cool for 5-10 minutes in the pan before removing them, Loosen the edges with a small spoon or knife and transfer the muffins to a cooling rack to cool completely.
While the muffins cool, melt the butter in one bowl and mix the cinnamon and sugar together in another.
Dip the tops of each sourdough donut muffin into the melted butter and then in the cinnamon sugar mixture. This will give them that true cake donut taste!
Any leftover sourdough donut muffins can be stored in an airtight container on the counter for 3 days or up to 1 week in the fridge.
