Cut the mushrooms and the onion in small strips.
Cut the parsley and the zucchini in small pieces.
Fry the onion in butter in a frying pan, add the mushrooms, parsley and the zucchini.
Add one inch each of the salt and the pepper.
Cook it all together and lower the heat and add the broth. Cook away the liquid.
Mash everything together and let it cool down.
Mix the egg whites to a firm foam and mix it slowly together with the vegetables.
Start the oven at 180 degrees Celsius.
Divide the mousse in 4 forms and place the forms in a bigger form.
Add boiling water in the bigger form so it covers almost to the edges of the small forms.
Place in the middle of the oven for 45 minutes.
Take out the mousse and turn them up side down on a plate and serve them together with a salad on the side.