Whisk the eggs in a bowl and season to taste with sea salt and freshly ground black pepper.
6 eggs, Sea salt and black pepper to taste
Heat a non-stick skillet over a medium heat, add 1 tablespoon of the cooking fat and cook the onions, leeks and mushrooms until the onions are soft, about 6 minutes. Reserve half of this vegetable mixture.
4 tablespoon leeks, 2 tablespoon onion, 1 tablespoon cooking fat, 6 mushrooms
Pour ½ of the egg mixture into the skillet with the vegetables that are still in the pan.
Use a spatula to stir the omelet gently while it cooks and to allow uncooked parts to run underneath.
When the omelet is set, fold the omelet in half and cook for another minute, covered.
Reserve and repeat the process for the other omelet.