In a food processor with metal blade, combine the melted chocolates, and the sugar, if using. Add the egg product, espresso, cognac, and vanilla. Cover and process with 4 or 5 on/off turns.
With the machine running, add butter, one piece at a time, through feed tube. Process until mixture is smooth. If necessary, refrigerate until spreading consistency.
In a medium mixing bowl, combine chocolates, sugar (if using), egg product, espresso, cognac, and vanilla. Beat smooth. Gradually add butter, beating until fluffy. (Note: This method will give a lighter, fluffier frosting.) Makes 2-1/2 cups.