Truffle Mashed Potatoes with Egg Yolk and Green Asparagus

Make mashed potatoes in the usual manner, but cook a little longer without peeling them and in a lot of salted water. Then peel the cooked potatoes, mash, put in a saucepan and add butter and hot milk. Salt where needed and add the thinly sliced truffle.
Clean the asparagus and sauté in a frying pan with a small amount of olive oil. When mashed potatoes have reached a creamy texture, remove from flame and place a couple of spoonfuls on each serving dish. Cook the egg yolk for a few seconds in boiling water with some drops of vinegar and place it in the centre of the mashed potatoes. Garnish with the asparagus and slivers of Parmigiano-Reggiano cheese.