Pour vegetable oil into a deep skillet until it reaches about 1 inch in depth.

Heat the oil to 360 degrees F.

In a medium bowl, combine buttermilk, egg, and hot sauce.

In a bag, mix together flour, cayenne pepper, and salt and pepper.

Pat the onion slices dry.

Dip the onion slices into the buttermilk mixture to coat them evenly.

Transfer the coated onion slices to the bag and toss to coat them with the flour mixture.

Deep-fry the onions in batches until they turn golden brown, approximately 2 minutes per batch.

Remove the fried onions and place them on a paper towel-lined plate to drain excess oil.

Sprinkle immediately with salt and serve hot.