If you are using the buttermilk substitution of 2 teaspoons vinegar plus remaining ¾ cup milk, mix that together first and let sit while you prepare other ingredients.
Using a hand mixer and a medium bowl or a stand mixer, combine sugar, oil and eggs. Mix until combined.
Add buttermilk, vanilla extract, salt and baking powder. Mix until combined.
Add flour, 1-1 ½ cups at a time. Mixing after each addition.
Turn out the batter on to a well-floured surface and thoroughly sprinkle the top of the dough with more flour. Use your hands to work the dough, adding more flour as needed, until smooth and not too sticky. Use a floured rolling pin to roll the dough until ¼-1/2 inch thick. See photo above.
Use a donut cutter, round cookie cutter, mason jar lid or empty can to cut out donut shapes. Save the centers to make as donut holes if desired. **see notes for ideas for household items to use as donut cutter. See photo above.
Place the donuts on a piece of parchment paper next to the stove where you will be frying the donuts.
Reroll the dough, adding additional flour as needed, to create more donuts.
Fill a dutch oven or medium-sized pot with 1-1 ½ inches of oil. Heat on medium heat for 2-3 minutes (or until the oil reaches 350-360 degrees, if you have a thermometer to check).
Gently place one or two donuts into the oil and flip them with a candy dipper or fork after 1-2 minutes or when they are browned. Cook the other side for 1-2 minutes then remove them from the oil and place on a cookie sheet to cool (I prefer to prep a cookie sheet with a cooling rack (photo above) to dry/cool the donuts).
Repeat until you have finished all of the donuts, then allow them to cool to room temperature before adding the chocolate glaze.