Overnight roast gammon

Method

1. Heat the oven to 240°C/220°C fan/gas 9. Cut 2 sheets of foil, roughly 60cm in length, and lay one over the other to make a cross. Sit the ham in the centre, then gather up the foil around it, folding the edges of the foil to seal tightly, leaving a gap at the top. Set on a wire rack in a deep roasting tin, then pour the cider through the gap and over the ham. Seal the gap, then cover the whole tin with another layer of foil, scrunching it tightly around the edges to seal tightly. Transfer to the oven and cook for 40 minutes.
2. Turn down the oven to 110°C/90°C fan/gas ¼. Slow-cook the ham for 12 hours (see Make Ahead).
3. Unwrap the gammon and discard the cooking juices (these will be very salty). Turn up the oven to 220°C/200°C fan/gas 7. Put the gammon on a baking tray lined with foil. Cut away the skin, leaving a good layer of fat, then pat dry with kitchen paper (this ensures a crisp, golden exterior). Brush with the dijon mustard and sprinkle over the sugar. Bake for 25-30 minutes until it has deep golden brown crust.
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5. For the sauce, heat the crème fraîche, parsley, English mustard and any cooking juices from the second bake in a medium pan until warmed through.
6. Slice half the gammon and divide among 4 plates. Serve with the watercress and parsley sauce.