Powdered Cake Doughnuts

Name: Powdered Cake Doughnuts
Ingredients: 2 quarts canola oil; 2 cups all-purpose flour plus additional for rolling; 1 1/2 cups cake flour; 1 cup sugar; 2 teaspoons baking powder; 1/2 teaspoon baking soda; 2 teaspoons kosher salt; 1/4 teaspoon nutmeg; 1 envelope (1/4 ounce) active dry yeast; 1/3 cup full-fat sour cream; 1 large egg plus 3 egg yolks, lightly beaten; 3/4 cup buttermilk, room temperature; 2 teaspoons vanilla; 1 to 1 1/2 cups confectioners' sugar