Season the flour with salt and pepper, and use to coat the lamb.
Melt half the butter with the oil in a large frying pan on the hob and fry the lamb, in batches, until browned. Transfer the browned meat to the bowl of the halogen oven. Add the onions to the frying pan and fry gently for a few minutes to soften. Pour in the stock and add the garlic, herbs and tomato purée. Season with a little salt and pepper. Bring just to the boil, then tip the contents of the pan over the meat in the bowl of the oven. Stir the ingredients together.
Set the temperature to 200°C (392°F) and cook for 1 hour until the lamb is tender.
Meanwhile, towards the end of the cooking time, melt the remaining butter in a frying pan and gently fry the carrots and turnips for 5 minutes to soften. Cook the beans in boiling water for 3 minutes.
Add all the vegetables to the bowl and cook for a further 20 minutes or until tender. Check the seasoning and serve in bowls with grainy bread or new potatoes.