Heat peanut or canola oil in a large heavy pot to at least 3 inches deep.

In a wide shallow bowl, whisk together all-purpose flour, ground cornmeal, cornstarch, and cayenne pepper.

In a separate bowl, beat an egg and buttermilk together.

Separate the sliced sweet onions into individual rings.

Working in batches, lightly toss the onion rings in the flour mixture.

Dip the floured onion rings into the buttermilk mixture, ensuring they are coated.

Allow excess buttermilk to drip off the rings.

Toss the buttermilk-covered rings again in the flour mixture, ensuring complete coverage.

Shake off as much excess flour as possible from the onion rings.

Carefully place the breaded onion rings into the hot oil.

Fry for 2 to 3 minutes, or until golden brown, turning occasionally to ensure even cooking.

Remove the fried onion rings from the oil and place them on a plate or bowl lined with paper towels to drain excess oil.

Sprinkle the hot onion rings with kosher salt.

Repeat the frying process with the remaining onion rings.

Serve immediately and enjoy the crispy, Southern-fried sweet onion rings!