Peel the potatoes, chop into even-sized chunks and cook in a large pan of boiling salted water for 15 minutes, or until tender.
Meanwhile, place the mince in a bowl with the mustard.
Coarsely grate in the apple.
Tear 75g of the bread crust into a blender and blitz into crumbs, then add to the bowl, season with sea salt and black pepper, and scrunch together well.
With wet hands, divide into four, then divide each piece into eight, and roll into 32 balls in total.
Bring the stock to a simmer in a large pan, then drop in the balls to poach for 5 minutes, or until cooked through.
Drain the potatoes, return to the pan, mash well with 1 tablespoon of extra virgin olive oil, then season to perfection.
Divide between warm bowls, then use a slotted spoon to scoop out the balls, sitting them on top.
Tear the soft inner part of the bread into the blender, with the soured cream and most of the chives.
Pour in 300ml of the stock and blitz until silky smooth and aerated.
Season to perfection, then divide between the bowls.
Finely chop and scatter over the remaining chives and drizzle with 1 tablespoon of extra virgin olive oil, to finish.