In a medium saucepan, pour in 2 cups of fresh apple cider and bring it to a gentle simmer. Reduce until it measures down to about 1/3 cup, about 15-20 minutes.

Whisk together 3 1/2 cups of flour, 1 tablespoon of cornstarch, 1 1/2 teaspoons of baking powder, 3/4 teaspoon of baking soda, 1 1/2 teaspoons of ground cinnamon, 1/2 teaspoon of fresh nutmeg, and 1 teaspoon of kosher salt.

Cream together 8 tablespoons of unsalted butter, 1/2 cup of granulated sugar, and 1/2 cup of brown sugar until light and fluffy, about 5 minutes.

Add 1/2 cup of sour cream and 1 tablespoon of vanilla extract, mixing until smooth. Then, add 2 room temperature eggs one at a time.

Gradually add the dry ingredients to the wet mixture, alternating with the reduced apple cider, beginning and ending with the dry.

Cover the bowl with plastic wrap and refrigerate for at least 2 hours, or overnight.

Roll out the chilled dough to about 1/2 inch thickness and cut out donuts.

Heat canola oil in a deep pot until it reaches 360°F.

Fry the donuts in batches for 1-2 minutes on each side, until golden brown, then drain on paper towels.

While warm, roll the donuts in a mixture of 1 cup sugar, 1 tablespoon cinnamon, and 1 teaspoon nutmeg.