Wash the clams and throw away any that are not closed, then soak them in cold salted water for 1 hour so that they release any sand they have inside.
Heat the oil in a wide casserole or pan with a tight-fitting lid. Put in the onion and stir over a low heat until it becomes very soft and is beginning to colour, then add the garlic and stir for another minute or so.
Add the beans, the wine and a little salt, mix gently and cook for 2-3 minutes. Place the clams on top, put the lid on, and cook over a medium-high heat for 3-5 minutes until the clams open.
Throw away any clams that do not open and serve sprinkled with the parsley.