Peel the tomatoes and cut into very small pieces.
Blend the tomato paste with the half the water and the flour.
Place the butter in a large, heavy-based casserole with the tomatoes, onions, veal, lamb, chickpeas, celery leaves, half the coriander and all the parsley, spices and salt to taste. Cover with water and cook for 15 minutes, then add the lentils.
Leave to cook for a further 10 minutes until everything is cooked through, then add the remaining measured water. As soon as it returns to a boil, add the diluted tomato paste and stir with a spatula for 10 minutes to prevent lumps from forming.
Add the rice 15 minutes before the end.
Serve sprinkled with the remaining coriander.