Place a cooling rack over a baking tray and set aside.
Place your frying oil in a dutch oven over medium heat. Use a candy thermometer to ensure you bring the oil to 350F.
Cut out the center of each biscuit and then stretch the biscuit a bit to make the hole and biscuit donut wider - approximately by 1/2".
Once oil is hot, fry each donut individually for about 1 minute per side, until golden brown.
Set each fried donut on the cooling rack to allow excess oil to drip off.
Once all donuts have been fried, turn off the heat for the oil.
Sift the powdered sugar into a large bowl.
Whisk in the milk, vanilla extract and salt.
Dip each donut into the vanilla glaze, then place back on the cooling rack and immediately sprinkle on sprinkles, if using.
Allow to sit until glaze is set, about 30 minutes.
You will need approximately 4 cups of oil to fry the donuts, but the amount will differ based on the size of your dutch oven or whatever you are using to fry them. You want at least 3-4" of depth. You can use peanut, canola or vegetable oil.