To make the filling, defrost the spinach, place it in a sieve and press on it firmly to extract as much excess liquid as possible; finely chop it then tip into a large bowl. Mix in the ricotta, eggs and cream.
Finely chop the spring onions and add to the bowl along with the parsley, dill, mint and garlic. Season well with salt and pepper and crumble in two thirds of the feta. Pour the mixture into the prepared pastry case and spread it level. Crumble over the remaining feta.