Egg:
Cook the duck egg in a water bath at 62C for two hours, once cooked turn the temperature down to 58 until needed.
Mushroom liquor:
Bash the mushroom trimmings with a rolling pin and leave out on a tray to oxidse. 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 over a bowl in a muslin cloth in the fridge over night 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. Poor 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 wont blend add a tiny amount of the reserved liquor to help get it smooth. Pass through a fine sieve and and keep in a piping bag until needed.
Pickled red onions:
Cut the onions into quarters leaving the root in. Bring the rest of the ingredients up to the boil and add the onions, remove from the heat and cover with cling film until cooled. Store the onions in the fridge in the liquor. When cooled separate the layers and remove the thin membrane from each layer. Slice thinly when needed and keep in some of the liquor.
Panko:
Toast the panko in foaming butter until golden, drain on Kitchen paper and grate lemon rind over the finished panko whilst still warm using a microplane, 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 whole 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, 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.