Step 1

To a large mixing bowl, add butter, sugar, and egg yolks, then use mixer to cream until pale yellow.

Step 2

Add sour cream and mix until blended. Mix in baking powder and salt.

Step 3

To another mixing bowl, add flour and cornstarch, whisking to combine well. Add flour mixture, about a cup at a time, mixing between each addition, until combined and no flour streaks remain.  Dough will be pretty sticky.

Step 4

Lightly spray the mixing bowl that had the flour in it with nonstick cooking spray, then line with plastic wrap. This is so the plastic wrap doesn't scoot around on you in the bowl.

Step 5

Transfer dough to plastic wrap and fold excess wrap over the top of the dough. Place in the refrigerator for at least 3 hours (or up to 3 days).

Step 6

Line a baking sheet with paper towels and top with a wire cooling rack. Set aside, on the counter next to your stove.

Step 7

Add oil to a heavy bottomed pot (a dutch oven works great here) and heat over MED heat until it reaches 365°F.

Step 8

While oil is heating up, lightly flour a work surface (I use my counter), and turn out the donut dough and remove plastic wrap. Lightly flour the top of the dough and roll out until about 1/2 inch thick.

Step 9

Use a donut cutter (or 3 inch biscuit cutter and 3/4-1 inch wide (at the base) piping tip), and cut out donut shapes. Brush any excess flour off the donuts.

Step 10

Carefully drop the donuts, a few at a time into the hot oil.  Fry about 1-2 minutes, or until golden brown and cooked through.

Step 11

Transfer cooked donuts to prepared wire rack, and cool.

Step 12

If frying donuts holes, they'll only need to fry about a minute per side. Transfer to rack and cool.

Step 13

To make the glaze, add powdered sugar, milk, and vanilla to small bowl and whisk until creamy and smooth.

Step 14

Dip each donut about halfway into the glaze, rotating right and left to coat.  Flip donut over and repeat with the other side.

Step 15

Return to wire rack so the glaze can set.