Vegetarian gratin recipe with courgette and ricotta and basil

Name: Vegetarian gratin recipe with courgette and ricotta and basil
Yield: Serves 6
Ingredients: 250g ricotta (fresh if possible); 1.75g courgettes (approx 8 medium); 4 1/2tbsp extra-virgin olive oil; 1 small red onion, finely chopped; 2 cloves garlic, very finely chopped; 250g organic mozzarella, drained; 3 medium eggs, lightly beaten; 50ml double cream; 80g pecorino, grated; 30g bunch of basil, leaves torn (discard the stalks); Generous grating of fresh nutmeg