Fry the onion in a pan with a little olive oil, soy sauce and truffle oil until soft and translucent. Set aside to cool.

Cut the Wagyu steak into strips and put them through a meat grinder to produce a fine mince.

Pour the kombu stock over the breadcrumbs and stir until it has all been absorbed.

Take half of the mixture and place in a food processor or blender and process too a smooth paste. Add the paste back to the chopped meat mix and use your hands to fully combine to a smooth mix.

Scoop out portions and mould into equal sized meatballs about 4 or 5 centimetres in diameter and place on baking paper lined tray.

Add some olive oil to a large frying pan and bring to a fairly high heat. Add a tablespoon of soft salted butter and wait for it to start foaming. Add the meatballs (in batches if necessary) and fry for 5-6 minutes spooning the hot butter over each meatball until nicely browned all over. Set aside.

For the broth, fry the chopped onion in a pan with a little olive oil until softened. Add the red wine and reduce by a third. Prepare 600ml of rich beef stock and add it to the broth with 80ml of kombu stock. Simmer for 30 minutes.

Pass the broth through a sieve and remove the onion before returning the liquid to the pan. Add the butter and whisk through to glaze the broth.

Add the meatball into the broth and re-heat for 5 minutes before serving.

Serve with mashed potato and wilted spinach or warm sushi rice.