Crack the eggs into a mixing bowl with a pinch of sea salt and black pepper. Beat well with a fork.
Heat a small knob of butter in a small frying pan on a low heat, and once melted and bubbling, add the eggs and move the pan around to spread them out evenly.
Quarter or roughly chop the mushrooms and add to a hot frying pan with a small knob of butter, a drizzle of oil and a pinch of salt and pepper. Fry and toss around until golden, then turn the heat down to medium.
Add the eggs and move the pan around to spread them out evenly. When the omelette begins to cook and firm up, but still has a little raw egg on top, sprinkle over the Cheddar.
Using a spatula, ease around the edges of the omelette, then fold it over in half. When it starts to turn golden brown underneath, remove the pan from the heat and slide the omelette on to a plate.
