Place the joint in a large saucepan. Add chopped vegetables and peppercorns. Cover with cold water. Bring to the boil, then simmer gently for approx. 20 minutes per ½ kg.
Set oven to 200ºC (400ºF/Gas 6). Remove the joint from the saucepan. Reserve liquid. Remove the rind and score the fat. Place the joint on a roasting dish. Spread with mustard and breadcrumbs, sugar and a knob of butter. Place in the oven for 15-20 minutes.
To Make the Sauce: Melt the butter, add the flour and mustard. Cook for a minute or two. Whisk in the cooking liquid and cream. Bring to the boil. Reduce the heat and simmer for 3-4 minutes. Taste for seasoning. The sauce should have the consistency of thin cream. Keep warm.
To Cook the Cabbage: In another saucepan cook the cabbage lightly with some of the cooking liquid. Drain well and toss in butter. Season to taste. Slice the bacon and serve on the bed of cabbage, a little of the mustard sauce and of course floury potatoes.