In a mixing bowl, combine 1 cup of flour, sugar, baking soda, baking powder, salt, and nutmeg.

In a separate bowl, whisk together buttermilk, melted butter, whole eggs, and egg yolk.

Pour the liquid ingredients into the dry ingredients while mixing on medium speed and beat for 10 seconds.

Add the remaining 2 cups of flour and mix until just combined, about 30 seconds.

Mix the dough thoroughly with a wooden spoon or spatula.

The dough should be moist and tacky.

Heat shortening and lard to 375F in a Dutch oven or heavy pan.

Dust a work surface and rolling pin with flour.

Roll out dough to 1/2-inch thickness.

Dip a 2 1/2-inch doughnut cutter in flour and cut out doughnuts.

Gather scraps, roll them out, and cut out more doughnuts.

Let doughnuts sit for 5 minutes.

Add doughnuts to oil, 4 or 5 at a time.

Flip doughnuts as they rise to the top.

Cook for 50 seconds, then flip again.

Fry for the same amount of time on the other side.

Drain on paper towels.

Let the oil return to 375F before frying subsequent batches.

Eat warm or dust with powdered sugar.