Wash chick peas, and cover with the water to soak for 12 hours, or overnight.
Bring to a boil in the water in which they were soaked. Boil gently for 2 hours,
add 1 teaspoon salt and cook until very tender, about 3 hours in all. Drain and reserve some of the cooking liquid.
Press peas though a food mill, adding about 2 tablespoons of the cooking liquid.
Slowly blend the tahini and most of the lemon juice into the puree.
Crush garlic with 1/2 teaspoon salt in a mortar and add to puree. Adjust flavor and consistency with lemon juice, cooking liquid, and salt, if necessary.
Spread in a shallow serving dish, swirling it with back of a spoon. Pour olive oil into center and sprinkle with parsley.