Cut the potatoes into chunks, cook until tender and then mash them. Fry the onions, add the green cabbage and fry it briefly with the onions. Crumble the pork scratchings and fried onions separately in a kitchen machine, then mix them together. Mix the cabbage with the potatoes, then add the hot milk and butter. Mash them all together. Season with salt and pepper.
Coarsely chop the oyster mushrooms and fry them in olive oil. Season with the Mushroom mix. Season with the gravy with the black garlic puree and salt and pepper. Pour the gravy evenly over the hotchpotch. Serve the oyster mushrooms on top of the hotchpotch and garnish with the pork scratchings and fried onions.