Cook the whole (unpeeled) potatoes in plenty of salted water for roughly 40 minutes or until they are soft. Drain, peel and mash potatoes with a potato masher whilst still warm, allowing mashed potatoes to fall onto a work top. Let to cool.
Form a well in the centre of the potato mass and fill it with flour and egg yolk. Season with salt and nutmeg, and quickly knead, mixing in all ingredients. Sprinkle some flour onto the work top and, with a little dough at a time, form long ropes, thencut them into bite-size pieces to make the gnocchi. Gradually arrange them onto a card-board tray sprinkled with a little flour.
Clean asparagus and cut stems into slices, leaving tips intact. Gently brown chopped shallots in a pan together with butter, add asparagus and 1/2 glass of water. Cover and cook for 5-6 minutes. Salt and add the Fontal cheese with Black Summer Truffle spread thinned down into a cream with a little warm water.
Cook gnocchi in salted boiling water. Remove them with a perforated ladle / colander (chinois) as soon as they float to the surface and place them in the sauce. Gently toss and serve piping hot, adding fresh black truffles shavings to taste.