The key to crispy, crunchy onion rings is in the frying. The oil must be hot enough every time you add a batch of onion rings, and there should be enough of it so that the batter has room to puff up as the onions cook. As with any fried food, the sooner you can get these on the table, the better. But you can also spread them on a baking sheet and keep them warm in a 250°F oven until ready to serve.
1Heat the oil (about 4 inches) in a large, heavy pot or deep fryer to approximately 365°F.
2Slice the onions into 1/4-inch-thick rings. Place them in a large bowl and cover with the buttermilk. Season with salt and pepper.
3Place the flour in a shallow dish and season with salt and pepper. Dip the onion rings into the seasoned flour, then dip them again in the buttermilk and again in the seasoned flour (this will be a messy process).
4Test the oil by dropping a small amount of batter into the hot oil—it should sizzle and brown quickly. Fry the onion rings in small batches until they are golden, 2 to 3 minutes. Let the oil come back to temperature before frying the next batch.
5Remove the onion rings with a slotted metal spoon and drain them on paper towels. Sprinkle them with a little extra salt if needed.
6Pile the onion rings in a tall stack on a serving plate and serve them immediately.
This recipe, while from a trusted source, may not have been tested by the CHOW food team.