In a small pan, warm the cream over medium heat till it feels hot, don't let it simmer. Place the chocolate in a heatproof bowl and pour the warm cream over top. Whisk till the chocolate melts. set bowl in ice bath till chilled. Place a piece of plastic wrap on the surface of the mixture and a second one over the bowl and place in fridge for 4 hours (can be done 1 day ahead) In the bowl with electric mixer fitted with whisk attachment, combine the cheese and half the white chocolate mixture and whip 2 minutes till mixed. Add he remaining chocolate mixture and mix on high till frosting hold a peak.
**Mascarpone cheese is from Italy and is sold in small tubs in most stores. Yield is approx but it is enough to frost 12-16 cupcakes.**Time indicated is chill time.