In a large mixing bowl beat together the cream, the cream cheese (both cold) and vanilla until thick and fluffy. Let the mixture stay at room temperature while melting the chocolate.
Chop or break the chocolate and put it in a heatproof bowl. Place the bowl over a pan with gently simmering water so the bowl doesn't touch the water (double boiler).
Mix the chocolate with dry spatula or spoon until melted completely (if 1-2 small pieces are remaining this is ok).
Remove the bowl from the heat and keep stirring gently with the spatula for 5 minutes so it cools down.
Transfer about 1 tablespoon of the cream cheese mixture to the melted chocolate. Whisk energetically to combine. Repeat 3-4 more times, until the resulting mixture is almost at room temperature.
Gently fold the chocolate into the rest of the cream cheese with the rubber spatula. Mix gently, until the frosting becomes uniform.
Notes
This frosting needs to be used right away: you can’t make it ahead and store it for future use. After used on a cake it can be frozen for up to 2 months.
For extra stable and sweeter White Chocolate Frosting you can double the chocolate quantity.
You can substitute the whipping cream with same quantity of sour cream. The frosting will become a bit thinner in this case so you can increase the white chocolate quantity or even double it.