You can use a stand mixer or a bowl with an electric hand mixer. Mix together flour, cornstarch, baking powder, salt, nutmeg and sugar in a bowl. In a separate bowl mix melted butter, eggs and sour cream/yogurt together.
Mix together both bowls until well combined, cover the bowl and chill for at least an hour (you can make the day before!)
When youre ready to make the donut, first put on your pot of lard (or other oil) to start heating up. You'll need 2 inches of oil in a heavy bottom pot. I like to use a cast iron dutch oven pot as it holds heat well. Over medium, you'll want to heat it to 325F.
While the oil is heating, get rolling out your dough! Roll the dough about 1/2 inch thick. Use a donut cutter or a canning ring with a water bottle top (I showed this method in my youtube video) Re-roll your scraps and cut out the rest. You should get around 2 dozen.
Fry the donuts making sure they have space, in my 6 qt dutch oven I can fit 7 donuts comfortably. Too many and they won't fry well. Fry about 2 minutes each side, careful not to let them burn and check your oil temperature every few minutes.
Take donuts out and place on paper towel. Flip them after a minute to soak up grease on the other side.
When you're done frying donuts, turn off oil, and remember you can use it a few times!