Preheat the oven to 350°F (180°C/Gas 4).
Put the plain flour into a plastic bag, season with salt and pepper, and add the rabbit. Shake until evenly coated in flour.
Heat the oil in a flameproof casserole and fry the rabbit until all the pieces are browned.
Stir in the sliced onions, garlic and mushrooms.
Add the port, stock, vinegar, parsley and tomato puree. Stir well, then bring the mixture to the boil.
Cover the casserole with a lid, transfer it to the oven and cook for 40 minutes.
Meanwhile, bring a saucepan of lightly salted water to the boil. Add the lentils and cook for 35 minutes until tender.
Spread the French bread with the olive puree.
Drain the lentils, stir them into the casserole and put the bread on top, with the topping uppermost. Dot with butter.
Return the casserole to the oven and cook, uncovered, for a further 10 minutes.
Serve garnished with lots of chopped parsley.