Beat the butter and cream cheese until smooth and creamy.
Slowly add ½ cup of powdered sugar at a time to the bowl and beat until mixed in well. Repeat with remaining sugar until all the sugar has been mixed into the butter and cream cheese.
When the mixture gets too thick add the creme fraiche slowly and beat in.
Beat for about a minute and add any remaining powdered sugar.
Once the last of the sugar is completely mixed in turn the mixer up on medium high and beat for two minutes.
Frost cooled cake immediately and refrigerate until ready to serve.