In a large mixing bowl, whisk together the all-purpose flour, granulated sugar, baking powder, baking soda, salt, and ground nutmeg.

Create a well in the center of the dry mix, then pour in the buttermilk, eggs, melted unsalted butter, and pure vanilla extract. Stir gently until just combined.

Cover the bowl with a clean kitchen towel and allow the dough to rest at room temperature for about 60 minutes.

Fill a deep fryer or Dutch oven with neutral oil and heat it to exactly 350°F (175°C).

Once the dough has rested, turn it out onto a lightly floured surface and roll the dough to about ½ inch thickness, then cut out shapes using a donut cutter.

Carefully place the donuts into the hot oil, frying them for 60 to 90 seconds on each side until golden brown.

Remove the donuts with a spider strainer and place them on a wire rack to cool.

In a separate bowl, whisk together the powdered sugar, additional buttermilk, vanilla extract, and a pinch of salt until smooth.

Dip each donut into the glaze and place them back on the wire rack for about 5 minutes to set the glaze.