The stalks from the mushrooms should be saved for soup tomorrow: i.e. boil them in milk with salt, pepper and nutmeg; liquidize and add double cream - serve.
Stuff the caps of the mushrooms with the mousse but don't fill them above the level of the rim.
Dust them in flour and dip in the egg mix. Then roll them in breadcrumbs.
Heat the oil to hot and drop them in.