Peel and slice the onions as thin as possible. You can also use a mandolin slicer to do this.

Place buttermilk in a large bowl. Add onions. Soak onions for about 5 minutes.

Meanwhile, heat oil for deep frying in a large saucepan.

In another bowl, combine together flour and cajun seasoning. Season with salt and pepper.

Remove onions from buttermilk.

Coat with flour and shake off excess flour. 

Working in batches, fry onion, stirring as needed and until evenly browned, for about 2-3 minutes.

Drain onions on paper towels.

Sprinkle with more salt if needed.

Store in an airtight container. 

Add as a topping for green bean casserole, or serve as a snack.