Start by peeling the Vidalia or 1015 onions. Slice them into thick rings, about ½ inch wide. Gently separate the rings and place them in a bowl.
In a large bowl, whisk together the flour, buttermilk, and water until smooth. The batter should be thick but pourable. If it’s too thick, add a bit more water until you reach the desired consistency.
Set up a breading station. In one bowl, place the cracker crumbs mixed with cornmeal. Dip each onion ring into the batter, letting the excess drip off, and then coat it with the cracker and cornmeal mixture. Make sure each ring is well-coated for maximum crunch.
In a deep frying pan or fryer, heat vegetable oil to 350°F (175°C). Use a thermometer to ensure accuracy.
Carefully place the coated onion rings in the hot oil, being careful not to overcrowd the pan. Fry them in batches until they are golden brown, about 2-3 minutes per side. Use a slotted spoon to flip them as needed.
Once the onion rings are a beautiful golden brown, remove them from the oil and place them on a plate lined with paper towels to absorb excess oil. Sprinkle with salt while they’re still hot for added flavor.