Beat eggs and water together. Season to taste. Put butter into omelette pan. Heat until sizzling but not brown. Swirl round to coat base and sides of pan.
Pour beaten eggs into pan. After about 5 seconds, move edges of setting omelette to centre of pan with a fork, knife or spatula. At same time tilt pan quickly in all directions so that uncooked egg flows to edges. Continue until mixture is lightly set and top is slightly moist.
Add Blue Cheese and onions. Remove from heat. Fold in half in the pan and slide out onto a warm plate. Garnish with parsley and serve immediately.
