Soak the chickpeas for one night.
The following day, drain the soaking water and replace it with enough fresh water to cover the peas well. Cook for one hour until soft.
Chop the carrot, celery, onion and potato into small cubes and sauté in the butter in a large heavy saucepan until translucent.
Take out about a mound of the soft cooked peas (mass based on a preparation for four people) and purée with a fork and add to the vegetable form. Add the remaining peas, the juice of one lemon, salt, saffron, Brussels sprouts, tomatoes and water as needed. Bring to a boil and gently toss with the lid closed.
Crush mustard, cumin and basil in a mortar and add to soup.
When the Brussels sprouts have reached the desired cooking point, stir in the cream, season with soy sauce and let stand for about 10 minutes before serving.