Recipe of the week: king oyster mushroom tagliatelle, slow-cooked duck egg yolk, mushroom ketchup, yeast

I saw this technique at WD50 and loved the simplicity of it. Wylie Dufresne and his team used to slice the mushrooms thinly on a meat slicer and then cut them into tagliatelle shapes before blanching them in emulsion to order and serving as if it was pasta. The look and texture were exactly what you would expect of perfect al dente pasta but with a beautiful delicate mushroom flavour.

We use the whole mushroom when we slice it, but cook it in the same way, served with a slowcooked egg yolk. It becomes the most perfect gluten-free pasta dish. We save all of the mushroom trimmings from our dishes and oxidise them to make our own mushroom ketchup, enhanced with soy sauce and sherry vinegar. This gives the dish real flavour.

Egg
4 duck eggs

Mushroom liquid
Mushroom trimmings
Light soy sauce
Sherry vinegar

Mushroom ketchup
500g mushroom liquid
8g agar-agar

Panko
100g panko breadcrumbs
50g butter
1 lemon

Yeast
50g dried yeast flakes
30g butter

Pickled red onions
2 red onions, peeled
100g white wine
250g white wine vinegar
70g caster sugar

Mushrooms
4 large king oyster mushrooms
100g butter
100g water
Extra virgin olive oil to taste

To finish
Watercress

Egg
Cook the duck egg in a water bath at 62°C for two hours. Once cooked, turn the temperature down to 58°C until needed.

Mushroom liquor
Bash the mushroom trimmings with a rolling pin and leave out on a tray to oxidise. When they go dark brown/black they are ready to use. Weigh an equal quantity of soy sauce to mushroom, and blend until smooth. Taste and season with sherry vinegar. Hang the mixture over a bowl in a muslin cloth in the fridge overnight to extract the mushroom liquid.

Mushroom ketchup
Weigh out the 500g of mushroom liquor and reserve what is left until later. Mix the liquor and agar together and bring to a full boil. Pour into a tray and leave to fully set. When firm, spoon into a blender and blend until silky smooth. If the mix is looking a little grainy and won't blend, add a tiny amount of the reserved liquor to help get it smooth. Pass through a fine sieve and keep in a piping bag until needed.

Pickled red onions
Cut the onions into quarters and leave the root in. Bring the rest of the ingredients up to the boil and add the onions. Remove from the heat and cover with clingfilm until cooled. Store the onions in the fridge in the liquor. When cooled, separate the layers and remove the thin membrane from each layer. Keep it in some of the liquor and slice thinly as needed.

Panko
Toast the panko in foaming butter until golden, drain on kitchen paper and, using a microplane, grate lemon rind over the finished panko while still warm. Season with sea salt.

Yeast
Toast the yeast until golden in the butter and drain onto kitchen paper. Season with sea salt.

To finish
Slice the mushrooms about 2mm thick using a mandolin or a meat slicer. Bring the butter and water to the boil. Add the mushrooms and cook for two minutes.

Crack the egg and separate the yolk, season with sea salt and ground black pepper, and place the yolk in the middle of the plate.

Drain the mushrooms, season and finish with a drizzle of olive oil, and wrap around the yolk.

Pipe small amounts of the ketchup around the dish and top with the yeast, panko and red onions. Finish with the peppery watercress.

• Read a review of Paul Foster's book, Salt*, here*

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