Prepare the onions: Peel the onions and cut off the tops. Make several vertical cuts into each onion, being careful not to cut all the way through, to create the 'blooming' effect.
Soak the onions: Place the onions in a bowl and cover with buttermilk. Let them soak for at least an hour.
Make the breading: In a separate bowl, combine flour, smoked paprika, garlic powder, onion powder, cayenne pepper, salt, and pepper.
Heat the oil: Heat vegetable oil in a large pot to 375°F (190°C).
Bread and fry the onions: Remove the onions from the buttermilk, letting the excess drip off, and dredge in the flour mixture, making sure to coat thoroughly. Carefully lower the onions into the hot oil and fry until golden brown and crispy, about 5-7 minutes. Remove with a slotted spoon and drain on paper towels.
