To make the cream cheese filling : While cake is cooling, whisk together the cream cheese, powdered sugar, butter and vanilla until smooth. If the filling is too thin, add a small amount more of powdered sugar. If the filling is too thick, add 1 or 2 tsp. of water. You want the filling to be easy to spread, but you don't want it to be too runny or it will ooze out of the cake as you re-roll it.