From the TLP test kitchen in Charleston, South Carolina
1 cup cider
5 tablespoons butter, at room temperature
1¾ cups sugar, divided
⅓ cup buttermilk
2 tablespoons maple syrup
3½ cups all purpose flour
1 teaspoon kosher salt
2 teaspoons baking powder
1 teaspoon baking soda
1½ teaspoon plus 2 tablespoons cinnamon
½ teaspoon nutmeg
4 cups neutral oil for frying
Pour cider into a small pan over medium heat. Cook until reduced by half, then set aside to cool.
In the bowl of a mixer fitted with paddle attachment, beat butter and ¾ cup sugar on medium speed until light in color. Scrape sides of bowl with a rubber spatula. Add eggs and turn on mixer, beating until incorporated. Scrape sides again with rubber spatula.
In a small bowl, stir to combine cider, buttermilk, and maple syrup. In a medium bowl, whisk to combine flour, salt, baking powder, baking soda, and spices. Scoop ⅓ of dry ingredients into mixer. Mix on low speed until incorporated, then add ½ of cider mixture and mix on low until incorporated. Scrape sides of bowl with rubber spatula and repeat, ending with dry ingredients. Mix on low until dough forms. Transfer dough to a sheet pan and chill in freezer 5 to 10 minutes. Meanwhile, pour oil into a medium pot over low heat.
In a medium bowl, stir to combine 1 cup sugar and 2 tablespoons cinnamon. Set aside.
Remove dough from freezer and place on a floured work surface. Roll to ½-inch thickness and, using a 3-inch round cutter, cut into rounds. Use a smaller cutter to remove center of round. Transfer cut dough to a clean sheet pan and reserve in refrigerator until ready to fry.
Increase heat on stove to medium and heat oil to 360 degrees. Gently place doughnuts in oil, being careful not to overcrowd pot. Fry until golden, approximately 4 minutes, then transfer to paper towels to drain. Toss in bowl of cinnamon-sugar to coat. Serve warm.