In a large mixing bowl, cream together the butter and sugar.
Add egg yolks and sour cream. Stir to combine.
Add flour, baking powder, sea salt, and nutmeg. Gently stir to form a batter.
Cover the bowl and refrigerate for at least one hour.
Remove the dough from the refrigerator and place it on a lightly floured surface.
Roll the dough out to a 1/2 inch thick circle.
Using the donut cutter, cut as many donuts out as possible, cutting close to each other so there is less to re-roll and cut.
Re-roll the left-over dough to 1/2 inch thickness and cut out more donuts. There should be a dozen donuts and a dozen donut holes cut total.
Place the cut donuts on a parchment paper lined sheet pan, cover with plastic wrap and refrigerate while heating the lard and making the glaze.
Begin melting the lard in a large stock pot over medium heat.
Monitor the temperature of the oil, it should maintain a temperature around 375℉.
In a medium sized mixing bowl, combine melted butter, milk, heavy cream, vanilla extract, powdered sugar, and sea salt.
Microwave the glaze for 20-30 seconds and stir. The glaze should be warm and slightly liquidy when glazing the donuts.
Once the oil is hot, gently drop 4 full size donuts into the oil.
Fry each side for about 2-3 minutes. Use the slotted spoon to flip the donuts halfway through frying and also to remove from the oil.
Place donuts on a paper towel lined plate after removing from the oil to cool slightly.
Continue frying the next batch.
While the second batch is frying, dip one donut at a time into the glaze. Flip the donut to glaze both sides.
Place the glazed donuts on a cooling rack to allow glaze to dry for at least 5 minutes before serving.
These donuts are best fresh but are still good one day after preparing.