1. Put the ham hocks in a large pan with the stock ingredients. Cover with cold water. Set pan over a high heat and bring to the boil. Reduce heat to a simmer, cook for 2 and a half to 3 hrs or until the meat falls from the bone. Leave to cool in the pan.Grease a 1-litre terrine mould or loaf tin with the oil, then line with cling film.
2. Remove the hocks, then strain the stock through a fine sieve into a pan. Set aside. Shred the ham, leaving some large chunks, removing as much fat and sinew as possible. In a large bowl, mix the ham with the mustard and parsley. Press the mixture into the prepared terrine.Bring the reserved stock back to a rapid boil and reduce by half. You should have about 600ml/1pt liquid remaining.
3. Remove from the heat. Meanwhile, soak the gelatine in cold water for 5 mins to soften.
4. Remove from the water, then squeeze out any excess liquid.
5. Add the gelatine to the hot stock and stir well.
6. Pour enough of the stock over the ham to just cover. Tap terrine firmly on a hard surface to knock out air pockets, then cover with cling film. Chill for 3-4 hrs or overnight. To serve, remove from the mould and carve into chunky slices.
7. Serve with caper berries and toast.