Preheat the oven to 170–180°C. Clean and wash the trotters thoroughly, and burn off any hair.
Fill a large deep ovenproof pan with water and bring to the boil. Blanch the trotters, then change the water and bring to the boil again. Add the trotters, the muslin bag of chickpeas, the bay leaves, leek, carrots and onion. Cover with a lid or foil and braise for 2 hours, until the meat is tender enough to fall off the bone but the trotters are still intact. Remove the trotters from the pan and discard the vegetables, but keep the chickpeas and cooking liquid. Pass the liquid through a sieve.
While the trotters are cooking, make the sauce: put the olive oil into a pan on a medium heat, then add the onions and cook until caramelized. Add the carrots, leeks and bay leaf and cook until all the vegetables are very soft and mushy (the longer you cook them the sweeter the sauce will be). Add the pancetta and chorizo and cook until they release their fat. Next add the sliced choriceros, dried chillies, smoked paprika and blitzed tomatoes, season with salt and pepper, and cook until the sauce begins bubbling: taste it and add sugar depending on how sweet the tomatoes are.
Season the trotters, then add to the tomato sauce with 1 litre of the sieved cooking liquid. Cook for another 30–40 minutes, until the flavours meld together: the gelatinousness of the trotters will make the sauce thick and sticky.
Serve one trotter, per person, with bread to scoop up the juices.