In a medium bowl, whisk together the flour, baking powder, baking soda, salt, nutmeg, and cinnamon until well combined. Set aside.
In the bowl of a stand mixer fitted with the paddle attachment, cream together the butter and sugar on medium speed until light and fluffy, about 2-3 minutes.
Add the eggs one at a time, beating well after each addition. Scrape down the sides of the bowl as needed.
With the mixer on low speed, gradually add in the dry ingredients just until combined. Do not overmix.
With the mixer still running, slowly pour in the buttermilk and vanilla extract. Mix just until incorporated, about 30 seconds.
Let the dough proof for 45-60 minutes until it doubles in size.
On a lightly floured surface, roll the dough out to ½ inch thickness and cut into rectangular strips.
Heat 3-4 inches of neutral oil to 350°F in a heavy bottomed pot.
Gently drop a few dough bars into the hot oil, frying for 1-2 minutes per side until golden brown.
Remove the fried donuts from the oil and drain on a paper towel lined baking sheet.
Let the donuts cool slightly before glazing.
Whisk together the powdered sugar and buttermilk until smooth, then add the vanilla and salt.
Dip the tops of the donuts into the glaze and let excess drip off.
