For the sauce: melt 40g of butter in a saucepan, add the flour and Stir. Add 40cl of the courgette stock. Keep kneading. Take the sauce off the heat and add the Parmesan. Mix the sauce with the courgettes.
Butter the mould(s)
Separate the eggs (put the egg yolk in the sauce and keep the egg whites aside). Mix in the olives and the chervil, add salt and pepper.
Whisk the egg whites until stiff, Fold into the mixture. Fill the moulds and bake for 30 minutes (20 minutes if you are using single moulds).