In a medium bowl, combine the flour, baking powder, baking soda, salt and cinnamon. In a separate bowl, whisk together the buttermilk and melted butter. In a large bowl, whisk together the sugar, egg, and lemon zest for several minutes until pale and thick. Add the flour mixture to the egg mixture, alternating with the buttermilk mixture to form a thick, sticky dough. Cover with plastic wrap and chill in the fridge for at least 1 hour and up to overnight.

On a lightly floured surface, roll out dough to about 1/2 inch thick. Cut into rounds with a floured 1 or 1 1/2 inch cutter.

Combine the sugar and cinnamon in a bowl and set aside.

In a heavy bottomed pot, add vegetable oil so that it's at least 2 inches deep. Insert thermometer and heat over medium-high heat to 375 degrees F.

Add the doughnut rounds a few at a time to the hot oil and fry until golden, about 2 minutes on each side.

Transfer doughnut holes to a paper toweled-lined plate to drain. While still hot, roll in the cinnamon-sugar. Enjoy immediately.