Wash the clams under cold water and rinse thoroughly, discarding any that are open or broken.
Heat the oil over a medium heat in a large saucepan. Add the garlic and fry for a few seconds until it just begins to colour. Add the clams and toss around briefly in the garlic and oil.
Pour in the manzanilla and add half the parsley, shaking the pan as you go. Simmer for about a minute to burn off the alcohol in the sherry.
When the clams are fully opened ( discard any that are closed) taste for seasoning- they may not need any salt.
Sprinkle over the remaining parsley and serve with lemon and lots of bread or toast.