1. Combine chickpeas and 1 teaspoon baking soda in a large bowl. Cover with cold water and stir to dissolve baking soda. Let stand at room temperature overnight. Drain and rinse chickpeas thoroughly.
2. In a large, heavy-bottomed pot, combine chickpeas, remaining 1 teaspoon baking soda, salt, onion, celery, carrot, garlic, bay leaves, and rosemary. Cover with water and bring to a boil over high heat.
3. Reduce heat and simmer, covered, until chickpeas are tender, about an hour and a half. Add water as needed to keep from boiling dry.
4. Discard onion, garlic, celery, carrot, bay leaves, and rosemary. Drain chickpeas, reserving their cooking liquid.
5. In a blender combine tahini, lemon juice, and a quarter of the cooked chickpeas. Puree thoroughly. Thin with reserved cooking liquid if necessary.
6. In a mixing bowl, combine tahini mixture with parsley and remaining chickpeas to serve.