Trim the asparagus by snapping off the base of the stems, then peel the spears from just below the tip. Blanch them in a large pan of boiling salted water for 3–4 minutes, then drain. Refresh in iced water until completely cold, then drain again and spread them out on a clean cloth. When they are dry, put them in the fridge.
For the vinaigrette, boil the truffle juice, chicken jus and vinegar together until reduced by half. Transfer the resulting liquid to a mixing bowl and allow it to cool. Add a small pinch of table salt and then, using an electric hand whisk on its slowest speed, add just a few drops of groundnut oil. Continue adding it very gradually, just a few drops at a time; the mixture should come together and start to thicken. This will take time; don’t be tempted into adding more than about half a teaspoonful at once. When all the groundnut oil has been incorporated, add the truffle oil in the same manner. Finally, adjust the seasoning and the consistency, adding a little water if the vinaigrette is too thick; it should be thick enough just to hold its shape.
Cut the asparagus into spears 14cm long, put them in a mixing bowl and toss with the olive oil, using just enough to coat them.
To serve, lie the asparagus spears neatly on serving plates, place the truffle shavings on top and, using two tablespoons, place a quenelle of the thick vinaigrette to the side. Garnish with the chervil sprigs and a pinch of Maldon salt.
An alternative to truffle juice…
Substitute a rich mushroom stock. Roast 400g of roughly chopped mushrooms – stems and all – in a medium–hot oven until lightly browned. Put them in a large pan and add water to cover; about 500ml. Bring to the boil and simmer for an hour. Then strain the mushrooms over a bowl, pressing them into the sieve to extract the maximum amount of juice. Return the liquid to the pan and put it back on the heat. Boil it until it reduces by half, and pass it through a fine sieve or chinois before use.