Step 1: Prepare the mushrooms

Heat the olive oil and half the butter in a non-stick frying pan over medium heat. Add the sliced mushrooms and cook for 3-4 minutes, stirring occasionally, until golden and tender. Season with a pinch of salt and pepper, then set aside.

Step 2: Beat the eggs

Crack the eggs into a bowl and whisk them with a fork until the yolks and whites are fully combined. Add a pinch of salt and pepper for seasoning.

Step 3: Cook the omelette

Melt the remaining butter in the same frying pan over medium heat. Pour in the beaten eggs and swirl the pan to spread them evenly. Allow the eggs to cook undisturbed for 1-2 minutes, until the edges start to set but the center remains slightly runny.

Step 4: Add the filling

Scatter the cooked mushrooms over one half of the omelette. Sprinkle grated cheese and chopped parsley on top if desired.

Step 5: Fold and serve

Using a spatula, gently fold the omelette in half to cover the filling. Slide it onto a plate and serve immediately.