Recipe: 60-day-aged beef tartare with sour onions and nasturtium capers

Serves 2

Sour onions

300g Roscoff onions, peeled and quartered

½ tsp salt

300ml whey

Nasturtium capers

1tbs salt

300ml water (for the brine)

100g nasturtium buds

100ml water (for pickle liquid)

100ml white wine vinegar

1tbs caster (superfine) sugar

Oyster emulsion

100g shallots, peeled and sliced

200ml dry white wine

125g fresh chucked rock oysters, juice reserved

150ml grapeseed oil

Oyster juice, to loosen sauce

Shallot crisps

150g butter, diced

150g banana shallots, peeled and finely sliced

Salt, to season

Beef tartare

250g 60-day-aged beef rump, trimmed and diced

1tbs Dijon mustard

1tbs nasturtium caper juice

1tbs extra virgin olive oil

Handful nasturtium leaves

Salt and freshly ground black pepper, to season

Place the onions into a jar with a seal-tight lid. Mix the salt with the whey and pour over the onions. Seal the jar and place in a store cupboard, out of daylight, to ferment for one month. They are ready when the onion starts to break down and they are acidic.

Nasturtium capers (prepare a week in advance)

Add the salt to the brine water in a pan. Bring to the boil until the salt is dissolved, then cool. Take a third of the brine and soak the buds for 24 hours. Drain, wash with cold water and repeat this process over three days. On the third day prepare the pickle liquid by adding the remaining ingredients to a pan. Bring to the boil, dissolve the sugar, then pour the liquid over the buds. Leave for at least three days.

Oyster emulsion (prepare on the day)

Add the shallots to a pan, pour over the wine and place on a low-medium heat. Boil until the wine has evaporated, remove and chill. Add the shallot mix and oysters to a blender and blend until smooth. Gradually add the oil until the mix is mayonnaise consistency. Add a little oyster juice to loosen the mix. Keep refrigerated until plating.

Shallot crisps (prepare on the day)

Place the butter in a wide, flat-bottomed pan on a high heat. Stir until the butter starts to foam. Add the shallots and cook, stirring, until the shallots start to brown and the butter smells like roasted nuts. Remove the pan from the heat and strain the shallots through a sieve.

Spread the shallot crisps on a flat tray on kitchen paper and season lightly with salt. Keep in a warm, dry place.

Plating the beef

Add the beef to a mixing bowl along with the mustard. Season with salt, pepper and the nasturtium caper juice, and finish with olive oil.

Place a large spoon of the oyster emulsion in the centre of the plates and spread it over the base of the plates with the back of a spoon. Scatter over the tartare, followed by a generous spoon of the nasturtium capers.

Next add the sour onion, in slices, over the top.

Dress some nasturtium leaves in the beef mixing bowl, add to the plates and finish with shallot crisps.

Recipe from London: The Cookbook (reviewed here). Photography by Jemma Watts