Heat 2 inches of oil in a deep-sided pan over medium to medium-high heat. Cut the onios into 3/4-inch-thick to 1-inch-thick rings.
Whisk together the sour cream and buttermilk and season with salt, pepper and chives. Pour the flour into a shallow dish and season it with salt and pepper as well. Double-coat the rings in buttermilk and flour. Add the rings to the hot oil and fry to crispy and golden, a few rings at a time.