Trim the courgettes and cut in half lengthways. Scoop out the centres, chop into chunks and reserve. Cook the courgettes in salted boiling water for 3-4 minutes. Drain and cool. Heat the butter and gently fry the onion and garlic for 3-4 minutes. Stir in the mushrooms and reserved courgettes, and half of the basil and cook for a further 2 minutes. Remove from the heat and cool slightly. Stir in half of the parmesan, the fromage frais and season to taste. Fill the courgettes. Sprinkle over the remaining basil and parmesan. Bake for 20 minutes on 200c.
