Prep: 10 minutes
Total: 20 minutes
2 to 3 cups neutral-flavored vegetable oil, for shallow frying
1 cup well-shaken buttermilk
1 small red onion, sliced into 1/8-inch thick rings
1 cup rice flour
kosher salt and freshly ground black pepper, to taste
1. Pour the oil into a pot (to should measure 1 1/2 to 2-inches up the sides of the pot); heat over medium heat until the temperature registers 375°F on a deep-fry thermometer.
2. Heat the oven to 200°F. Line a plate with paper towels.
3. Pour the buttermilk into a bowl and add the onions; separate the rings with your fingers, swirling them until well-coated.
4. Pour the flour into another bowl. Transfer the onion rings to the flour in small batches, tossing to coat evenly. Transfer the rings, tapping off any excess flour, to a baking sheet or large platter.
5. Carefully add six to eight onion rings at a time into the oil and cook until lightly browned on one side, 30 to 60 seconds. Turn quickly and gently using tongs, chopsticks, or a slotted metal spoon; cook for 30 to 60 seconds more. Place on the prepared plate to drain any excess oil and season immediately with salt and pepper. Fry the remaining onion rings. Keep warm in the oven until ready to use.