Heat oil in a large soup pot. Add onion and celery and saute over moderate heat until golden.
Add potato, carrots, bouillon cubes, celery leaves, tomatoes, and cumin. Cover with 6 cups of water and bring to a boil.
Lower heat and simmer gently over medium heat, covered, for 15 minutes or until the vegetables are nearly tender.
Add the cauliflower and continue to simmer for 10 minutes more, or until it is crisp-tender. Season to taste with salt and pepper and remove from heat.
Let the soup cool, then refrigerate overnight, to allow time for it to develop flavor.
Just before serving, heat the soup through. Add remaining ingredients and simmer over very low heat for 10 to 15 minutes. Add more water if the vegetables seem crowded, then adjust seasonings. Yield: 8 Servings.
Note: For matzo balls, you will need a box of Passover matzo ball mix on which you'll find a standard recipe for matzo balls. Increase the recipe so that there will be 3 or 4 matzo balls for each serving of soup. If you'd like, substitute an extra egg white for 1 or 2 of the egg yolks called for in the recipe.