Start off by making the yeast mixture first. In a large measuring cup, add 1 cup of warm milk (108 degrees Fahrenheit), 2½ tsp dry active yeast, and 2 tablespoons of granulated sugar.
Whisk it up and let it froth up for about 5-10 minutes.
Add all dough ingredients into your stand mixer
Now, in a stand mixer, add 3 1/2 cups all-purpose flour, 1/2 cup granulated sugar, 1/2 teaspoon salt, 3 tablespoons unsalted butter, room temperature, 1 large egg, 2 large egg yolks, 1/2 teaspoon vanilla extract, and the frothy yeast mixture.
Using the hook attachment, begin mixing the dough on low speed. Once there are no more dry patches of flour visible, pick the speed up to high. Continue mixing the dough for about 10-15 minutes. Yes, it takes time to get the right dough consistency. The dough should be just a little sticky and tacky to the touch.
Let the dough rise
Then take the dough and place it into a large greased bowl (I greased mine with 1-2 teaspoons of olive oil).
Cover the dough with plastic wrap and let it rise for about one to two hours or until it doubles or even triples in size. The more the dough rises, the fluffier your donuts will be.
Roll, cut, and rise the dough again
Once the dough is done rising, punch it down and place it onto a floured surface. Then use a rolling pin to roll the donut dough to about 1/2 inch thick.
Now cut out circles using a 3-inch biscuit cutter or glass cup. After you’ve cut out the donuts, reshape the scraps, then roll them out and cut out some more circles. You should get about 16 donuts from the recipe.
Place the cut out donuts onto a baking sheet lined with parchment paper. Then cover them with a thin kitchen towel or plastic wrap and let them rise for 30 minutes.
Fry the donuts and cover in sugar
In a heavy-bottomed pot, heat 2 inches of corn oil to 340 degrees Fahrenheit. I recommend using an instant-read thermometer to monitor the oil temperature.
Now fry each donut for about 2 minutes per side. You want them to be golden brown. Then use a large slotted spoon to transfer the fried donuts to a baking sheet lined with paper towels.
Once the fried donuts cool to a warm temperate, roll them in a bowl of granulated sugar. 1 cup of sugar should be more than enough for all the donuts.
TIPS for making these donuts
Use warm milk with the yeast. In order to activate the yeast so it froths and makes the donuts fluffy, you need the milk to be about 108 degrees Fahrenheit. If the yeast doesn't froth, your milk may not have been the right temperature or the yeast might be expired. Discard and try again.
Mix the dough for the full 10-15 minutes. I know it's tempting to rush the dough mixing because it looks combined, but make sure it continues to mix the entire time. This working of the dough is what gives the donuts the right consistency.
Let the dough rise for more time rather than less. During the first rise, the donut dough should double or even triple in size. The more time you allow it to rise, the fluffier and airier your sugar donuts will be. Allow them to go the full 1-2 hours.
Use an instant-read thermometer for the frying oil. Keeping the oil temperature at 340 degrees Fahrenheit consistently is crucial because it ensures that the donuts cook through and also don't burn. A thermometer can help you check the oil periodically