Pre-heat the oven to 220ᵒC. Take a large roasting tin and place the sliced onions, rosemary and garlic into the centre in a pile.
Prepare the pork by patting dry with kitchen roll. If the skin has not already been scored by your butcher, take a sharp knife and score lightly with lines roughly 1cm apart. Take some sea salt and rub it all over the pork, getting right into the score lines in the skin.
Place the pork on top of the onions and rosemary. Put the roasting tray into the oven for around 30 minutes, or until you see the skin puffed up and golden. Remove the pork from the oven, cover with foil, and turn down the heat to 170ᵒC. Place the tray back in the oven and cook for a further 2 hours before removing and allowing to rest for a minimum of 20 minutes.
To make the salt baked potatoes, mix together the rock salt, egg whites and smoked paprika. Put a layer of the salt mixture into a deep baking tray, then place the potatoes on top. Cover with the remaining salt mixture and bake the whole thing in the oven for 45 minutes to 1 hour, using a knife or skewer to check whether the potatoes are cooked in the middle. Remove from the oven once cooked and allow to cool for 10 minutes.
Mix the mustard and mayonnaise together in a small bowl. Turn out the potatoes in their salt crust and smash in order to release them. Brush off the majority of the salt crust before serving. Carve the pork and place the watercress into a big salad bowl. Serve everything family style and enjoy!
Our thanks to www.watercress.co.uk for providing this recipe
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