2) Preheat the oven to 170C/Gas 3. Remove the meat from the refrigerator and leave to sit at room temperature for 30 minutes before cooking. Roast the pork for 3 1/2 hours, uncovered, until the outside is crispy-brown (it should look like mahogany). Let the meat rest on a cutting board for 10 minutes before slicing.
3) While the pork is cooking, prepare the coleslaw. Combine the mustard, mayonnaise, sour cream, lemon juice, vinegar and sugar. Mix well and add finely sliced savoy cabbage, purple cabbage, spring onions and carrots. Season with salt and pepper, to taste, cover with clingfilm and set aside in the refrigerator until you are ready to serve.
4) To serve, cut the brioche buns in half and pile up some sliced pork. Top with a large spoonful of coleslaw and place the top half of the bun on top. Garnish with parsley.