To make the salsify tagliatelle, wash the salsify well in cold water. Use a vegetable peeler to make tagliatelle ribbons by shaving along the length of the salsify. Leave the ribbons to soak in a bowl of ice cubes for at least 30 minutes.
To make the cheese and wine sauce, sweat the shallot in a frying pan with the butter. Deglaze with the wine and cook until the liquid has evaporated. Add the cream and bring to the boil. Remove the pan from the heat and stir in the cheese. Use a handheld blender to blitz, then push the mixture through a conical strainer or sieve. Season to taste with salt and pepper.
Drain the salsify ribbons. Gently reheat the cheese sauce in a deep saucepan and add the salsify ribbons. Cook for 1 minute, cover with a lid and cook for 1 more minute. Taste and adjust the seasoning. Coat the salsify tagliatelle in the sauce.
To serve, divide the cooked buckwheat between wramed bowls and spoon over the salsify tagliatelle. Drizzle with olive oil and add a twist of pepper and a grating of truffle. Serve immediately.