Make the donut dough

• In a large bowl add 3 tablespoons of unsalted softened butter along with 1/4 cup granulated sugar, and 1/4 golden brown sugar. Mix it really well using an electric hand mixer.
• Then add 2 large egg yolks and 1/2 teaspoon of vanilla extract. Mix it again once more.
• Now, in a separate bowl sift together these dry ingredients: 2 cups 1/2 cup all-purpose flour, 2 teaspoons baking powder, 1 Tablespoon cornstarch, ½ teaspoon salt, and 1/4 teaspoon ground nutmeg.
• Now add 1/3 of the flour mixture to the butter and sugar mixture and begin working it in with a spatula.
• Then add a third of your sour cream (so 1/2 cup at a time). Mix again.
• Then add the second third of the flour mixture, mix again, then add another 1/2 cup of sour cream, mix.
• Now add the last third of the flour, mix, then add the last 1/2 cup of sour cream. The dough will seem very sticky, but don't worry this is what you want to see. Too much flour will result in a dense and dry donut.
• Place the donut dough into a large sheet of plastic wrap and cover it tightly. Refrigerate for 1 hour or until firm. You can place it in the freezer to speed things up if you want!
• Now generously dust your work surface and place the chilled dough on top. Add additional flour on top of the dough as well. Begin rolling out the donut dough to about 1/2 inch thick. 
• Now use a donut cutter or 2 different sized biscuit cutters to cut out as many donuts as possible. I used a 3 1/2-inch circle cutter and 1 1/4-inch circle cutter. It helps to dip the cutters in flour to prevent sticking.
• Now reshape the scraps, roll it out again to 1/2 inch thick, and cut as many donuts out once more. Repeat this step as needed. I got about 14 donuts.
• Fill a heavy-bottomed pot with about 2 inches of corn oil and bring the oil temperature to 325 degrees Fahrenheit.
• Carefully fry the donuts in batches for about 2 minutes per side. Keep a close eye on them to avoid burning them. Also, make sure to adjust the heat according to the thermometer. If it brings to climb too high, bring the heat down a notch.
• Once the donuts are fried, transfer them to a plate lined with paper towels to absorb the extra oil.
• Now, for the glaze, mix 3 cups powdered sugar, 1/2 cup salted butter, melted, 1 teaspoon vanilla extract, and 4 Tablespoons hot water.
• Dip the donuts in the glaze and let them set on a cooling rack. Then enjoy them with a cup of coffee or a glass of cold milk.