Cauliflower cheese gratin with leeks

Method

1. While the lamb is in the oven (or up to 12 hours ahead), put the milk, peppercorns, onion, bay leaves and mace in a non-stick saucepan. Bring to the boil, then set aside for 30 minutes to infuse.
2. Bring a large pan of salted water to the boil. Cut the green leaves off the cauliflower and reserve any with small, pale green stalks. Discard the rest. Break the cauli into large florets and cut the leeks into 2.5cm pieces.
3. Meanwhile, make the white sauce. Bring the infused milk back to the boil, then strain it into a jug. Discard the flavourings and wash out the pan, then add the butter and melt over a low heat. Stir in the flour and cook gently for 30 seconds. Remove the pan from the heat and gradually stir in the milk. Return to the heat and bring slowly to the boil, stirring all the time. Simmer for 10 minutes.
4. Put the cauliflower in the boiling water and cook for 4 minutes or until just tender (it will cook further in the oven.) Remove with a slotted spoon to a colander and drain well. Add the reserved leaves and leeks to the boiling water in the pan and cook for 2 minutes, then drain well.
5. Arrange the cauliflower florets, leafy stalks and leeks in a shallow ovenproof dish. Season the white sauce with salt and pepper to taste, then stir in the cream. Pour the sauce over the vegetables and sprinkle with the grated cheese.
6. Bake at 180°C/160°C fan/gas 4 for 35-45 minutes until lightly golden.