Donuts:

2 3/4 c cake flour
1 1/2 tsp baking powder
1 tsp salt
1/4 tsp baking soda
2/3 c sugar
2 Tbs butter
1 Tbs shortening
3 egg yolks
3/4 c sour cream
1 tsp vinegar

Glaze:

3 c powdered sugar
1⁄3 c +1 Tbs c milk
1 Tbs corn syrup
2 1⁄2 tsp vanilla
1/4 tsp salt
Vegetable oil for frying

Instructions  :

Donuts:

–  In a medium sized mixing bowl combine cake flour, baking powder, salt and baking soda. Set aside. In the bowl of a stand mixer fitted with a paddle attachment combine sugar, butter and shortening. Beat on a medium-high speed until smooth. Add in eggs and mix until just incorporated. Add sour cream and vinegar and mix to combine. Add in the flour mixture and mix until just combined.
–  Transfer the dough into a greased bowl and cover with plastic wrap. Place into the fridge to let chill for 30 minutes. Towards the end of the chill time, preheat 3” of oil in a large stock to 375°. Once the dough has been chilled, turn it out onto a clean, floured surface. Press the dough out into a 3⁄4” thick disc. Use a donut cutter to cut out as many donuts as you can. Form the remaining dough back together and repeat the process until all the dough has been used.
–  Carefully place 2-3 donuts into the preheated oil and fry for 1 1⁄2-2 minutes, before flipping and frying for an additional 1 1⁄2-2 minutes. Once fried, carefully remove the donut from the pot and place into a cooling rack. Repeat the frying process with the remaining donuts.

Glaze:

In a large mixing bowl combine powdered sugar, milk, corn syrup, vanilla and salt. Whisk together until smooth. Dip the warm donuts into the glaze, then place into a wire cooling rack to let the excess drip off.