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 incorporat 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.