Peel and slice the pink Roscoff onions into thin rounds. Chop the garlic and parsley and set aside in a bowl. Cut off the mushrooms’ stems and clean them.
In a frying pan, brown the onions, mushrooms, garlic, and parsley with a knob of the butter. Set aside.
Cut the slice of cured ham into strips.
Break the eggs and separate the whites from the yolks.
Add a pinch of salt to the whites and beat until stiff. Pour the cream in with the yolks.
Season with salt and pepper and mix. Add some of the stiffened egg white to the yolks, and gently mix with a rubber spatula.
Pour into the remaining egg white and mix
Put the mixture into a baking dish. Preheat the oven to 180°C.
Arrange the vegetables on the omelette and bake for 15 minutes.
Upon serving, add the strips of cured ham