Heat the oil in a frying pan. Add the spring onions and mushrooms, fry for approx. 3 mins. Add the fennel and peas, season and continue to cook for approx. 5 mins. Stir in the crème fraîche and chives.
Preheat the oven to 60°C, warm the platter and plates. Blanch the spinach in boiling salted water for approx. 1 min., rinse in ice-cold water for approx. 1 min., drain and squeeze out. Mix the flour and salt in a bowl and create a well in the middle. Blend together the milky water, egg and spinach, gradually pour into the well while mixing with a whisk, continue to whisk until the batter is smooth. Cover and leave to stand at room temperature for approx. 30 mins. Heat a little butter in a non-stick frying pan. Pour 1/8 of the batter into the pan, reduce the heat. Once the underside is cooked and separates from the pan, turn the omelette, finish cooking and keep warm in the oven. Repeat these steps with the remaining batter.
Place the omelettes on the plates, spoon the filling on top, fold over and sprinkle with cress.