Prepare the filling: Heat the olive oil in a small pan over a medium heat. Add the sliced mushrooms and diced red pepper. Sauté for 3-4 minutes, stirring occasionally, until the mushrooms are soft and have released their moisture (you will see the pan become less steamy and the mushrooms will take on a light golden colour on their edges). Remove from the heat and set aside to cool slightly.

Whisk the eggs: Crack the three eggs into a mixing bowl. Add the milk, a generous pinch of sea salt, and a few grinds of black pepper. Whisk vigorously for a full 45 seconds using a fork or a balloon whisk. You are looking for a uniform, pale yellow liquid with a slightly frothy surface. The mixture should run off the whisk in a smooth, consistent stream without any stringy white bits attached.

Heat the pan: Place a 20cm non-stick frying pan over a medium-low heat. Add the unsalted butter. Swirl the pan gently as the butter melts. You want it to foam and then settle into a quiet, gentle sizzle. The butter should smell nutty and turn a very light golden brown, but it must not smoke or turn dark brown. This should take about 30-40 seconds.

Pour and cook the base: Pour the whisked eggs into the centre of the pan. Do not stir immediately. Let the eggs sit for 5 seconds, then use a silicone spatula to gently push the cooked edges towards the centre, tilting the pan so the raw egg runs into the gaps. Repeat this motion for about 45 seconds to 1 minute. The eggs should be mostly set but still look very soft and glossy on top, like a thick custard that jiggles slightly when you shake the pan.

Add the filling: Sprinkle the grated cheddar cheese down the centre third of the omelette, leaving a 2cm gap at the top and bottom. Spoon the sautéed mushrooms and peppers over the cheese. Scatter the chopped chives and parsley on top of the vegetables.

Fold the omelette: Using your spatula, carefully lift one side of the omelette and fold it over the filling. Gently slide the spatula under the other side and fold it over the first fold, creating a neat, tight cylinder. The seam should be on the bottom. The omelette should look plump and golden, with the cheese just starting to melt and ooze slightly from the ends.

Roll onto the plate: Tilt the pan over your serving plate. Using the spatula to guide it, gently roll the omelette seam-side down onto the plate. The surface should be glossy, unbroken, and a uniform golden yellow. You should hear a faint, soft sizzle as it settles onto the warm plate.

Garnish and serve: Immediately scatter the fresh rocket or watercress alongside the omelette. Squeeze a tiny amount of lemon juice over the greens. Finish with a final crack of black pepper over the top of the omelette. Serve at once, while the centre is still wonderfully soft and the cheese is molten.