Begin by melting the butter in a medium mixing bowl. Add the sugar and mix until they are combined, then stir in the 2 egg yolks.

Mix in the vanilla extract and sour cream until they are well-mixed and the mixture is smooth.

In a separate bowl, stir the cake flour, baking powder, and salt together.

Add the dry ingredients to the wet and mix until the donut dough is mixed thoroughly. It should fairly stiff but not dry–like a soft cookie dough. Wrap the dough in a sheet of plastic wrap, patting it out into a disc so that it’s easier to roll out.

Chill the dough for at least an hour, or up to two days if you’ve used double-acting baking powder. When you are ready to fry the donuts, remove the donut dough from the refrigerator.

On a lightly floured sheet of parchment paper, roll out the dough until it’s 3/8″ thick. Cut as many circles as you can out of the dough with a 3.5″ cutter, then use a small cirle (about 1″) to cut another hole in the center. Alternatively, you can use a donut cutter.

Press the remaining edges together, then reroll the dough and cut out the rest of the donuts.

Frying the Donuts

Pour a neutral-flavored oil with a high smoke point (see recipe notes below) into a fairly deep pot. This protects your hands and kitchen from a lot of hot oil splatter. I add about 2 quarts of oil (about 3-4 inches deep in a 6-quart pot.

Heat your oil to 350°F-375°F over medium heat. It may take a while to get to temperature, but be patient! Once the oil gets hot, it stays that way for a while and you don’t want to have to wait for it to cool down again. Adjust the temperature of your burner if it seems like the oil is getting hot too fast or if it’s getting too cool when you start adding donuts.

Once the oil is up to temperature, use a metal slotted spoon to carefully lower 2-3 donuts into the oil–if you add more, it’ll lower the oil temperature too dramatically. They may sink at first but should float after a few seconds.

Cook the donuts for 1 1/2 to 2 minutes, or until they are a deep golden brown.  Flip them over, and allow the donuts to cook for the same amount of time on the other side.

When the donuts are finished cooking, place them on a cooling rack with a baking tray underneath to catch any oil that might drip off.

Glazing the Donuts

In a small pot, heat the milk until it’s steaming but not boiling. Whisk in the sifted powdered sugar, a little at a time.

Stir in the vanilla extract. Dip each donut in the glaze, then use a fork to flip it.

Remove the donut from the glaze, allowing the excess to drip off. Set it on a cooling rack until the glaze has hardened.