Skin and fillet trout; reserve trimmings. Refrigerate fillets until chilled.  Place trimmings in chilled blender or food processor; season with salt.  Process for 30 seconds or until smooth.  Add small amount of cream; process until mixed.  Strain through fine sieve into stainless steel bowl set in ice.  Slowly incorporate remaining cream; whip to stiff peaks.  Season with cayenne pepper.  Spread thin layer of mousse over chilled fillets.  Seal in plastic wrap; steam for 5 to 6 minutes.  Remove plastic wrap; sprinkle with brioche crumbs.  Grill until golden.