Thirty minutes before making the frosting, place the cream cheese and butter on the counter. Cut the butter into four pieces and coarsely chop the white chocolate., Place the chocolate in a heatproof bowl and melt in the microwave in 15-second bursts, stirring in between, until the chocolate is 85% melted. Stir without further heating until the chocolate is completely melted. Let cool until just slightly warm to the touch (80°F to 85°F); a digital thermometer is a helpful tool here., Place the cream cheese, butter, and crème fraîche (or sour cream) in the bowl of a food processor and process until smooth and creamy., Scrape down the sides of the bowl. Add the cooled, melted white chocolate and pulse several times to incorporate. Add the vanilla and pulse until it disappears., Use the white chocolate frosting to decorate carrot cake, cupcakes, or any spice cake. Store any leftover frosting, covered, in the refrigerator for up to 1 week; freeze for longer storage.
