Line baking sheet with parchment. Line a large plate with paper towels. In a paper bag, combine cup sugar and 1 Tbsp. cinnamon; shake to mix well. Set aside.
Bring cider to a boil over medium heat. Cook, stirring occasionally, about 10 minutes.
In a bowl, mix baking powder, salt, 1 cup flour and remaining sugar and cinnamon. In another bowl, whisk butter, eggs, yolk and cooled cider. Add cider mixture to flour mixture; mix until smooth. Add remaining 2 1/2 cups flour and mix. Dough will be sticky. Refrigerate 20 minutes.
Pour oil into a large pot and heat oil over medium-high heat until it reaches 375ºF.
Remove dough from fridge and roll out to 1” thick with donut cookie cutters cut out donuts. Makes about 24 Donuts.
Carefully place doughnuts into hot oil. After about 1 minute, doughnuts will rise to surface and begin to brown. turn over and fry 1 1/2 minutes longer. Transfer to lined plate to drain.
When doughnuts have cooled for 1 minute, add to plate with cinnamon sugar and toss to coat.