Prepare the Dry Mixture

In a small mixing bowl, combine the cake flour, baking powder, salt, and ground nutmeg. Sift the ingredients thoroughly to ensure even distribution and a smooth texture in the dough.

Cream the Butter and Sugar

Using a large bowl, cream the softened butter and granulated sugar until the mixture achieves a sandy consistency. Incorporate the egg yolks, mixing thoroughly to form a cohesive batter.

Combine Ingredients Alternately

Gradually incorporate the dry ingredients into the wet mixture in three portions, alternating with the sour cream. Begin and end with the dry mixture to ensure proper blending.

Chill the Dough

Shape the dough into a disc, wrap it securely in plastic wrap, and refrigerate for approximately one hour. Chilling will make the dough more manageable for shaping.

Shape the Donuts

On a floured surface, roll out the dough to a thickness of about half an inch. Utilize a donut cutter or two round cutters of varying sizes to create approximately 12 donut shapes.

Fry to Perfection

In a heavy-bottomed pot, heat about two inches of canola oil to 325°F. Fry the donuts in small batches, cooking each side for about two minutes. Transfer the donuts to a plate lined with paper towels to absorb excess oil.

Prepare and Apply the Glaze

In a shallow bowl, whisk together the powdered sugar, light corn syrup, salt, vanilla extract, and hot water until the glaze is smooth. Dip each donut into the glaze, ensuring complete coverage on both sides. Place the glazed donuts on a wire rack set over a sheet pan, allowing the excess glaze to drip off. Let the donuts rest for 15-20 minutes until the glaze sets.