Cut the zucchini lengthwise into quarters, then into 2.5 cm (1 in) pieces. Heat the oil in a heavy saucepan and cook the garlic and zucchini slowly for approximately 25 minutes until the zucchini are brown and very soft. Add salt, pepper and the stock, and simmer for another few minutes. Remove from the stove.
Put three-quarters of the zucchini in a food processor and purée. Return to t