Slice the onions into rings and separate them gently.
Discard any small inner portions or save them for another recipe.
In a large bowl, mix the buttermilk and hot sauce.
Add the onion rings and ensure they are fully coated.
Refrigerate for 45 minutes to 1 hour.
Combine the flour, baking powder, black pepper, cayenne pepper, and salt in a shallow dish.
Mix thoroughly.
Heat vegetable oil in a frying pan to 375 degrees F.
Ensure you have enough oil to submerge the onion rings fully.
Dip each buttermilk-soaked onion ring in the flour mixture.
Shake off excess flour.
Fry in hot oil until golden brown and crispy.
Remove and drain on paper towels.