Preheat the oven to 160°C.
Butter a piece of kitchen foil and wrap the Yorkshire pot completely.
Place leek halves in a roasting tin, top with the wrapped pot, and roast for 150 minutes.
Remove the pot from the oven and discard the foil.
Increase oven temperature to 200°C.
Roast pot for 15 more minutes until golden and juices run clear from the center.
Rest the meat for 15 minutes before carving.
Boil halved potatoes in salted water for 4 minutes and drain.
Fry potatoes in melted lard on the hob until they start to brown.
Season potatoes with salt and roast in the oven at 200°C for 60 minutes.
Infuse milk with clove-studded onion in a bowl over simmering water until just below boiling.
Discard the onion and cloves while keeping the milk over the heat.
Whisk in breadcrumbs until the sauce thickens.
Season with nutmeg, salt, white pepper, and cayenne.
Stir in butter and double cream until melted then keep warm.
Boil cranberries, apples, water, cloves, and cinnamon in a saucepan.
Simmer for 15 minutes until fruit is tender and berries split.
Strain the mixture through a muslin-lined sieve into a bowl without pressing the fruit.
Mix in sugar and vinegar.
Heat liquid to 104°C, cool, then transfer to a sterile jar.
Boil sprouts in salted water for 10 minutes and drain.
Fry pancetta in olive oil until crisp and golden.
Toss sprouts with the cooked pancetta to warm through.
Carve meat slices and serve with potatoes, sprouts, bread sauce, and jelly.