Start by feeding the sourdough starter: Use active sourdough starter. Starter should be ripe. Use a rubber band to mark your starter after feeding, and observe when it reaches its peak.

Preparing the dough: Into the bowl of a stand mixer, add room temperature whole milk. Now add the ripe sourdough starter and mix well in the milk to form a smooth paste. Add the sugar and mix well. Further add in the vanilla extract, salt, and melted butter. Mix everything well. If you are going to add some nutmeg, go ahead and add some. Now add the flour. Combine with the help of a ladle or a fork.

Kneading the dough: Now place the bowl on the stand mixer, and start kneading at low speed for 6-7 minutes. It will look super sticky initially. Now, bump up the speed, and knead for additional 6-7 minutes or until the dough becomes smooth and supple. It should leave the sides of the bowl completely. If it does not comes together and you feel that the dough is still very sticky, add 1-2 tablespoons of flour and knead again.

Bulk rise: Transfer the dough to a greased bowl with enough room for it to rise. Cover with a cling wrap or kitchen towel and let it bulk rise at 70-85 0 F for 2 hours. Now place the bowl in a refrigerator for cold retarding the dough. Cold proof it for 8- 12 hours.

Rolling the dough and shaping the Doughnuts: Remove the dough onto a flour-dusted work surface. Gather the sides and make a roundish ball. Now use your hands to flatten it. Switch to a rolling pin and start rolling the dough into a ½ inch thick layer. Keep dusting some flour under it occasionally, so that it does not stick. Now cut the Doughnuts using a cookie cutter or a donut cutter. Use the smallest cookie cutter to make the central hole.

Proofing the Doughnuts: Cover these sourdough doughnuts with a kitchen towel, and let them proof till they become puffier. It should take about 1 hour or longer if your kitchen is cooler.

Frying: In a pan heat vegetable oil deep enough to fry the sourdough doughnuts. The oil temperature should be around 320-330 0F. Gently lift the doughnuts and drop them into the oil. Doughnuts should take about 2-3 minutes to cook from one side. Then, gently flip them and cook on the other side for the same time.

Topping or dressing: If you are planning to just coat them in cinnamon sugar, drop them into the sugar-cinnamon when they are right out of the oil.