Heat oil in a large heavy pot. It should be at least 3 inches deep, but more is better.
In a wide shallow bowl, whisk together flour, cornmeal, cornstarch and cayenne. In a second bowl, beat egg and buttermilk. Separate onion slices into rings.
Working in batches, lightly toss the rings in the flour mixture, then dip into the buttermilk mixture. Allow most of the liquid to drip off, then toss again in the flour mixture. Shake off as much flour as possible and place the rings into the hot oil.
Fry for 2 to 3 minutes or until golden brown, moving the rings around a bit in the oil to keep them separated.
Put the onion rings on a plate or bowl lined with paper towel and salt. Repeat until the onions are done.
Oahu Fresh provides access to food from local farms for homes, offices, restaurants, hotels, and schools throughout Hawaii. As an avid participant in the CSA Hawaii program, we take pride in delivering freshly grown produce to you.