Dry Ingredients: In a small bowl sift together the cake flour, baking powder, salt, and nutmeg.

Wet Ingredients: In a large mixing bowl, beat the butter and sugar together until well combined (the texture will be sandy). Add the egg yolks and mix well.

Combine in batches: Add the dry ingredients in three batches, alternating with the sour cream, and ending with flour.

Chill: Wrap the dough in plastic wrap then chill for 1 hour.

Form Donuts: Remove the dough from the fridge and roll it out on a floured surface to about 1/2 inch thickness. Use a donut cutter (or two round biscuit cutters) to cut as many donuts out as possible. You should get around 12.

Fry: Pour about 2 inches of canola oil into a heavy bottomed pot. Heat the oil to 325° F. Fry 2-3 donuts at a time, being careful not to overcrowd the pot. Fry for about 2 minutes on each side, then remove to a paper towel-lined plate.

Glaze: Whisk together glaze ingredients in a shallow bowl, until smooth. Place a wire cooling rack above a sheet pan. Dip donuts in the glaze, covering on each side, and place on the wire rack. Let sit for 15-20 minutes until glaze is set.