Throw out clams that are cracked or broken. If any clams are slightly open, tap them on the counter. If they don’t close, throw them out. Rinse under cool water, rubbing off any dirt with your thumbs.
Add the clams, cover with a lid, and simmer until the clams open, about 10 minutes. Add the cubes of butter to the pan, stir, and scatter with parsley.
While the clams cook, cut several thick slices of bread, rub the garlic clove over the surface of the bread, brush lightly with olive oil, and sprinkle with salt. Toast on a hot grill or under a broiler until lightly browned. This should only take minute or two. Set aside to serve with clams.
Spoon clams and broth into shallow bowls with a slice of bread on the side.