Decadent indeed, this frosting is a chocolate lover's dream come true. Creme fraiche offsets some of the richness. Use it to frost vanilla cake (or chocolate if you're a chocoholic).
Beat cream cheese and butter with a mixer on medium speed until pale and fluffy, about 3 minutes. Sift together sugar, cocoa powder, and 1/4 teaspoon salt; gradually beat into cream cheese mixture. With machine running, pour in melted chocolate in a slow, steady stream. Beat in creme fraiche until well combined. If frosting doesn't seem firm enough, refrigerate for 10 minutes. Beat before using.