For the ox tongue, bring all of the brine ingredients to the boil. Remove from the heat and allow to chill

Place the tongue in a vacuum bag, cover with the brine and seal in a chamber sealer. Leave for 7 days to cure

After 7 days, wash in clean, cold water, place in a fresh vacuum bag and seal once more

Preheat a water bath to 64°C

Cook the tongue for 36 hours in the water bath. Once cooked, remove and chill. Do not finish preparing the tongue until you're almost ready to serve to prevent oxidisation

Preheat the oven to 150°C/gas mark 3

To prepare the smoked onion oil for the mayonnaise, coat the spring onions in a dash of oil, then cook in a skillet until lightly charred

Cut the shallots in half lengthways and coat with oil. Deeply caramelise the shallots in a pan until very dark and charred

Place the shallots and onions in a tray and roast in the oven until cooked through. Peel the shallots, chop the onions then place in a container and cover with the grapeseed oil. Leave to infuse for 24 hours then strain through a fine sieve

To make the mayonnaise, combine the egg yolk, mustard, salt and pickled onion juice in a small bowl. Slowly whisk in 250g of the infused onion oil until emulsified

Mix together all of the ingredients for the tartare with ½ tsp of the smoked onion oil

Remove the tongue from the bag, remove the outer skin and cut into thin ribbons on a meat slicer

To serve, arrange the tartare in a ring on the bottom of the plate and pipe dots of the smoked onion emulsion around. Pile the ox tongue on the beef and garnish with the pickled onions, mushroom slices and watercress