1. Cut onions into 1/2"-thick slices, and separate into rings. Pour buttermilk into a bowl. Combine flour and cornmeal in another bowl and season liberally with cayenne, salt, and pepper.

2. Pour oil into a heavy skillet to a depth of 3" and heat over medium-high heat. Dip a few rings into buttermilk, shake off excess, dredge in flour mixture, shake off excess, then repeat, coating again with both buttermilk and flour mixture.

3.When oil is very hot (375°), add onions and cook until golden, about 3 minutes. Drain on paper towels and sprinkle with salt. Fry remaining onions in batches.