Slice a large sweet onion into 1-inch rounds and separate the rings, or trim and peel several shallots, then make cuts almost to the root to allow them to fan out.

Whisk together flour, paprika, garlic powder, onion powder, cayenne pepper (if using), salt, and black pepper in one bowl. In a separate bowl, whisk buttermilk and egg until combined.

Dip each onion piece in the buttermilk mixture, then transfer to the seasoned flour, pressing to coat thoroughly. Shake off excess flour and place coated onions on a wire rack.

Heat about 2-3 inches of vegetable oil to 350°F (175°C) in a large, heavy-bottomed pot or Dutch oven, using a thermometer to monitor the temperature.

Carefully lower a few coated onion pieces into the hot oil, frying for 3-5 minutes until golden brown and crispy, turning occasionally for even cooking.

Remove fried onions and place them on a wire rack over a paper towel-lined baking sheet to drain excess oil. Immediately sprinkle with extra salt if desired, and repeat with remaining onions.

While onions fry or cool, whisk all ingredients for the Classic Buttermilk Ranch Dip together in a small bowl until smooth. Taste and adjust seasonings as needed.