In a small skillet, saute shallots in butter until tender. Remove from the heat; cool.
Meanwhile, in a large bowl, combine the cheeses, sour cream, Cognac, salt and pepper. Add shallots and mix well. Line a 3-cup bowl with plastic wrap. Spread cheese mixture into prepared bowl. Cover and refrigerate for at least 1 hour.
Unmold onto a serving plate; garnish with walnuts. Serve with crackers.