Heat butter in a non-stick frying pan of about 20 cm. Add egg mixture to the pan. Cook the eggs over medium heat until they are set.
Spoon filling onto one half of the omelette. Sprinkle cheese over. Gently fold the half without filling onto the other half to close. Heat through, cook the omelette for about 2 – 5 minutes and serve hot. Garnish with fresh herbs.
Substitute mushrooms with half a chopped red or green pepper.
Substitute onion with leeks or chives.
For a meaty omelette, add cooked; 125 g chopped bacon, sausages or mince.