Rated M, 107 minutes

★★★★

Italy's most introverted and unpredictable filmmaker appears to have cast a female version of himself in this movie with the marvellous Margherita Buy playing an introverted and unpredictable filmmaker who's falling apart in the middle of making a film.

Nanni Moretti has often cast himself, playing someone close to himself in his movies, as in Dear Diary (1993) or The Son's Room (2001). His preoccupation with psychoanalysis is another reason critics lazily call him the Italian Woody Allen; that, and his flair for comedy. He played an atheist shrink brought in to help a newly elected and anxiety-ridden pope (Michel Piccoli) in We Have a Pope (2011). What we did not know at the time was that Moretti's mother was dying during the making of that film. So now we have Mia Madre, in which Moretti examines his sense of loss and panic at the death of a parent. For those of a certain age, there can be no more universal story.

This is not strictly a comedy, as you can guess, although it has a couple of hugely funny sequences. John Turturro​ arrives in Rome as megastar Barry Huggins to play the lead in the film that Margherita (Buy, using her real name) is directing – a neo-realist political drama about workers taking over a factory after an American tycoon has bought it. Huggins tries to proposition her when she picks him up at the airport. Huggins is an ego in search of meaning, so things only get worse. Turturro is hilarious in the role, which is lucky, because the film is inevitably sad, sadder, saddest.

The idea itself seems very Italian. "A harried movie director retreats into his memories and fantasies." That is the description on IMDb of Fellini's 8½, but it could just as easily be this film. The movie shooting goes awry when Huggins can't remember his lines. Margherita's personal life is in tatters. Her mother Ada (Giulia Lazzarini) has been hospitalised; Margherita is completely unaware of the dramas in the life of her teenage daughter Livia (Beatrice Mancini); Margherita's affair with actor Vittorio (Enrice Ianniello) is over. Her dreams begin to plague her, and the sense of linear time disappears. Moretti jumps in and out of memory without the usual visual cues to tell us what period we are looking at. It's easy enough to work out, and a compliment that he assumes we can follow.

Complicating further, Moretti plays Margherita's brother Giovanni. Most of his scenes are in the hospital, as their mother slips away. He is practical, where his sister is fanciful; when she brings tasty snacks from the deli, he turns up with a full meal he has made himself. When the doctor explains what is about to happen, she can't accept the bad news, but he accepts the truth. Giovanni is the guy Moretti wants to be; Margherita is the person he really is, in other words.

Moretti's films are never predictable: the beauty can come from anywhere. There is a scene here where Margherita and her ex-husband (Stefano Abbati) teach Livia how to ride a scooter, each parent acting as a bollard she must ride around. It seems like nothing, but it is both symbolic and natural, a grace moment in Margherita's unravelling life.

The prestigious Cahiers du Cinema named Mia Madre as the best film of 2015 – from anywhere. (Hint: make a film within a film and the French will eat it up). I would not go that far, but it is a significant achievement. It could be a little faster, a tad more upbeat, a pinch funnier, but Margherita Buy's performance takes it to a high plane of emotionalism. She has superb truthfulness, especially in despair. Moretti was right to change the character to a woman – that gives us three generations of women of the same family – and Margherita never feels like a man's emotions in a woman's body.

For Moretti, it's partly a film about feeling inadequate, something he says he always feels when making a film. That may surprise those who love his films, but it does explain one of his great strengths as an artist – his humility, the sense that he is exploring when he makes a film, rather than explaining.

Mia Madre opens on May 5