Wash the cauliflower and broccoli, separate the florets from the stem and chop them bite-sized. Use the stems for other purposes. Wash the tomatoes, remove the stems, peel and core them and work them into small cubes. Use the cooking water to blanch cauliflower and broccoli (cook for 5 minutes), then separate 100 g and make the stock with the vegetable stock. Place the well-drained florets on a serving bowl.
Cap the onions and the cloves of garlic at both ends, peel and roughly cut into pieces. Wash the peppers, cut in half lengthways and core one half and cut into small cubes.
Fry the onions and garlic cloves in the olive oil until the onions begin to brown. Add the tomato pieces and fry for 3 minutes. Deglaze with the vegetable stock along with the tomato and lemon juice. Add the chili peppers and the chopped olives. Let the mixture boil down until creamy.
Stir in the celery leaves and season with the pepper and salt. Add the sauce to the florets, garnish and serve as a side dish (contorni) or with white bread as a snack between meals.