Heat a large amount of oil in a deep heavy pot. Place a good amount of flour in a large bowl. Peel, wash, dry and trim the ends the onion. Place flat side down and cut into thin slices. Toss the onion pieces into flour and lightly coat. Place a mesh colander over a large pan and pour onion pieces in the colander to remove excess flour. Gently pour onion pieces into the hot oil and cook until cgolden brown, turning occasionally to keep browning even. Use a slotted spoon to quickly remove onions to a paper towel lined plate. Allow to cool. Onions will crisp-en as they cool.