Over moderate heat, melt the 3 tablespoons of butter in a heavy 3 or 4-quart soup pot. When the foam subsides, add the chopped onions, carrots and celery and cook, stirring almost constantly, until the vegetables are wilted but not brown. Pour in the stock, add the optional ham bone and the bouquet, and bring to a boil. Then lower the heat and, with the pot half covered, simmer slowly for about 1/2 hour.
Add the chickpeas, the ham, the broad beans (or string beans), and the cubed potatoes and continue to simmer until the potatoes are tender. Remove the ham bone. Season the soup with salt and freshly ground pepper, to taste, and serve sprinkled with chopped parsley in large, deep soup plates.
Recipe courtesy of Michael Fields, Culinary Classics and Improvisations, Random House, 1967