Stand the potato gratin for 20 minutes before serving to allow it to cool slightly, thus helping the layers stick together and therefore easier to cut.
Want more ideas on how to cook pork to perfection? Visit Yahoo!7 Food
Preheat oven to 200C.
Combine salt, caraway seeds and garlic, then rub into pork, making sure to get into scored cuts.
Arrange onion in an ovenproof roasting dish and top with pork. Roast for 30 minutes.
Remove from oven and reduce temperature to 170C. Arrange apple around pork, and then pour half the beer over pork. Return to oven and roast for a further for 2-3 hours.
To make potato gratin, stir cream, blue cheese and garlic in a small saucepan over medium heat until cheese is melted and combined. Season with salt and pepper.
Arrange potato, seasoning between layers and overlapping tightly, in a greased baking dish. Pour cream mixture on top. Cover tightly with foil.
Bake for 1 hour or until tender. Remove foil and sprinkle with tasty cheese. Bake for a further 30 minutes or until cheese is golden and bubbling. Remove from heat and set aside for 20 minutes.
Remove pork from oven and baste with remaining beer. Increase temperature to 220C and roast pork for 30 minutes. Remove and set aside, partially covered, on a warm plate to rest.
To make sauce, add 500ml of boiling water to baking dish to deglaze. Bring to the boil, scraping any crust off base of dish. Simmer until mixture has thickened to form a sauce. Using a stick blender, blend until combined. Season with salt and pepper.
To prepare cabbage, heat oil in a large frying pan. Add onion and bacon to pan and cook until soft. Add cabbage and cook, stirring occasionally, until tender.
Place pork knuckles on serving plates, then add potato gratin and red cabbage. Drizzle with sauce to serve.