Put the garlic, apple juice and cleaned mussels in a pan, and season. Bring to the boil, cover with a lid and simmer for 5 minutes, shaking the pan frequently. The mussels will open when cooked - discard any that do not. Mix the cornflour into the cream, add to the pan and stir. Bring back to the boil, shake again and cook for 1 minute more. Spoon the mussels and sauce into bowls and sprinkle with the chopped parsley.