Remove and discard dark meat from fish fillets. Flake white meat, and set aside.
Beat cream cheese at medium speed with electric mixer until fluffy. Add lemon juice, cognac, and pepper; beat until thoroughly blended. Stir in fish, onion, dill, and capers. Pack into 1-quart crock or bowl; cover and chill two hours. Let stand at room temperature 15 to 30 minutes to soften; serve with crackers or crostini. Garnish, if desired.