For the mousse, combine the water and Parmigiano Reggiano in a heavy based saucepan. Bring to the boil, stirring occasionally, and then simmer for five minutes. Remove from the heat and allow to sit until the solids are settled. Strain off the liquid into a clean pan, pushing down well on the solids. Measure the liquid and reduce if necessary to give 150g.
In a small bowl, whisk together the egg yolk and mustard, then whisk in the hot Parmigiano Reggiano liquid and return to the pan. Cook out as a custard. Add the soaked gelatine and pass through a fine chinois into a clean bowl. Allow to cool and then season to taste with salt, pepper and lemon juice. At this stage it wants to taste a little strong as the whipped cream will reduce the intensity. Whip the cream to soft peaks and fold into the mousse base. Refrigerate to set.
To make the garlic crumb, heat the olive oil in a small non stick pan and add the garlic. Stir to break up the garlic, then add the breadcrumbs. Cook over a medium heat until the crumbs are golden brown. Season with salt and pepper, remove from the heat and stir in the parsley. Tip onto paper towel and set aside to cool.
Trim the asparagus and blanch in boiling, heavily salted water. Drain and toss with a little salt and olive oil.
To serve, lay four spears of asparagus on the plate. Use a warm spoon to form a large quenelle of the mousse and place on top of the asparagus. Scatter some garlic crumb over the asparagus.
Dress with olive oil and Parmigiano Reggiano shavings.