Step 1

Press 1/2 cup white sugar and butter together in a bowl until crumbly. Add egg yolks and stir until well combined.

Step 2

Sift flour, baking powder, and salt into a separate bowl. Place 1/3 of the flour mixture and 1/2 the sour cream into the sugar-egg mixture; stir until combined. Mix in the remaining flour and sour cream. Refrigerate dough until ready to use.

Step 3

Mix 1/3 cup sugar and cinnamon together in a bowl.

Step 4

Roll dough out onto a lightly floured work surface to 1/2-inch thick. Cut 9 large circles in the dough; cut a small circle out of the center of each large circle to create doughnut shapes.

Step 5

Preheat an air fryer to 350 degrees F (175 degrees C).

Step 6

Brush 1/2 of the melted butter over both sides of the doughnuts.

Step 7

Place 1/2 doughnuts into the basket of the air fryer; cook for 8 minutes. Paint cooked donuts with the remaining melted butter and immediately dip into the cinnamon-sugar mixture. Repeat with the remaining doughnuts.