Brush piece of beef with mustard, roll in Parmesan and seasoning.
Roll in cling film and place in freezer to firm. Remove and slice very thinly with sharp knife or on slicing machine.
For the mousse, place yolks, garlic, vinegar, salt and pepper in blender. Blitz until fine, then emulsify with oil and add boiling water. With remaining boiling water melt gelatine and add to mix. Then add Parmesan and blitz again.
Pass through a sieve and allow setting. Fold in whipped cream and place in fridge for 2 hours until set.
Finally combine all batter ingredients, add one slice of very thin onion.
Coat onion in batter and deep fry quickly.
Finish dish with little balsamic dressing, sprinkle with sea salt and olive oil.