Wash the clams and put them in a big frying-pan with half a tumbler of cold water. Bring to the boil. As the clams start to open transfer them, still in their shells, to a suitable pot. When the process has been completed, strain and keep the water.
Heat the olive oil in a pan. Add the onion and the garlic. When they are golden-brown add the breadcrumbs and let them brown a little too.