Heat a large pot or Dutch oven on medium heat. Roughly chop the onions and celery and chop them finely in the food processor, and add them to the pot along with the olive oil and salt. Allow them to sauté for 3-5 minutes before adding the carrots.
Roughly chop the carrots and chop them finely in the food processor. Add the carrots to the pot with the onions and celery.
Add the spices to the pot, and cook, stirring, for 30 seconds or until you can smell the spices.
Add the water. It should be enough to barely cover the vegetables. Bring the pot to a boil, then reduce the heat and cover the pot with a lid. Allow the soup to simmer for 15-20 minutes, or until the carrots are tender.
Measure the tahini and add approximately 1 litre of the soup to the tahini. You can do this in a measuring jug, and blend with an immersion blender, or you can use a regular blender or food processor - although food processors don't always do well with liquid, so be careful.
Add the creamy tahini and carrot mixture back to the soup pot and stir to combine.
Serve this soup with something nice for dipping. Toppings optional.