Sift dry ingredients together into a medium sized bowl and set aside. (flour, baking powder, salt, and nutmeg.)

In a stand mixer, use paddle attachment to mix sugar and shortening for 1 minute on LOW speed, until the texture of sand.

Add egg yolks and mix for 1 minute more on medium. Scrape down the sides of the bowl as needed with a rubber spatula. Mixture should be light colored and thick.

In three additions, add the DRY ingredients to the WET alternating with sour cream. Mix until just combined on LOW speed. Scrape down sides of the bowl as needed. The final dough should be sticky, and look like a cookie or biscuit dough.

Place dough in a clean bowl covered with plastic wrap, and chill for 45 minutes or up to 24 hours.

Place paper towels on a cooling rack, and place aside.

Use a deep fryer, large pot, or high-sided pan filled with at least 2"/ 5cm of canola oil. Use a candy thermometer to bring the oil to 325 degrees F/165 degrees Celsius. (May take at least 15+ minutes.)

Generously spread flour on a cutting board or countertop, and begin rolling. Flour the dough on top and rolling pin as needed. The dough should measure 1/2" thick for best results.

Dip the doughnut cutter into flour before each cut, and proceed to make as many doughnuts and holes as possible. Gently fold the dough scraps together to make additional doughnuts and holes. Floured hands make the work less sticky.

Shake extra flour off dough before placing in the oil, and cook a few at a time to avoid crowding.

Once doughnuts FLOAT, fry 15 seconds.

Gently flip, fry for another 75-90 seconds, until golden and cracked.

Gently flip again, fry the first side for another 60-75 seconds until golden.

Place doughnuts on cooling rack lined with paper towels. Cool slightly, and proceed with glazing while doughnut is still warm.

As first batch of doughnuts is done frying, begin making the glaze.

In a stand mixer with paddle attachment, mix ingredients together on LOW speed until smooth and all the sugar is incorporated.

Scrape the sides of the bowl as needed. If glaze seems too thick, slowly add more hot water 1 teaspoon at a time.

Dip one side of each hot doughnut into warm glaze.

Place on another cooling rack. Let dry for 10-15 minutes before serving.