Use a fork to steady the onion. Slice into 1 cm rings. Remove the skin and separate the rings. Discard the ends and the small rings right in the centre.
Heat the oil in a 18 x 9 cm saucepan until really hot and slightly bubbling. The oil should be deep enough to fully cover the onion rings. I used 2 cups.
Place all the dry ingredients in a bowl and mix. Add the wet ingredients to another clean bowl and mix to combine. Dip each onion ring in the wet and then into the dry to fully coat and place on a wire rack. Coat 8 at a time and fry in batches of 4 to avoid the whey batter soaking and disappearing into the egg.
Carefully lower 4 onion rings at a time into the hot oil and fry about 45 seconds or until golden and crisp. Remove the onion rings with a slotted spoon and place on kitchen paper to soak up any excess fat.
Repeat for all the remaining onion rings.
