Place the flour,baking powder, baking soda, cinnamon and salt in a medium bowl, stir to combine.
Place the eggs and sugar in a large bowl. Beat for about 3 minutes until the mixture is very thick and light in color. Beat in the orange zest and vanilla. Pour the melted butter in a slow steady stream into the the mixture while beating. Beat until all the butter is incorporated.
Add the sour cream to the bowl in 2 additions, beating well after each addition.
Gently FOLD the flour into the mixture in 4 additions. The dough may be sticky, cover the dough with a kitchen towel and let sit for an hour.
Sprinkle 2 cookie sheets with flour. Using a third of the dough, pat the dough out to about 1/2 inch thickness on a lightly floured surface. Using a 3 inch wide biscuit cutter, cut dough rounds out. Cut the hole out of the middle of the dough with a small round. I used the cap of my vanilla extract bottle to cut the middle hole.Place the dough rounds on the floured cookie sheets. Repeat with the remaining dough using 1/3 of the dough at a time to roll and cut the doughnuts out.
Heat 4 inches of vegetable oil in a heavy duty metal pot with high sides. Heat the oil to 350 - 365 degrees. Fry the doughnuts one or two at a time until golden brown. Remove from the oil and drain well, cool slightly before adding a glaze.