Drain clams, saving juice. Add bottled clam juice to the drained juice to make 5 cups of liquid (add water if short).
Heat oil over medium and cook onion until it has softened, about 5 minutes.
Meanwhile, scrub the potatoes and cut them into 1/2-inch pieces.
Stir the garlic into the oil-onion mixture. Cook about 30 seconds. Stir in flour to coat vegetables. Gradually whisk in the liquid. Stir in the potatoes, bay leaves and thyme. Bring to a simmer. Cook about 15-20 minutes or until potatoes are tender.
Stir in clams, cream and parsley. Turn to a simmer briefly--just to heat everything, not to boil. Remove from heat. Throw out bay leaves. Season with pepper if desired.