White Chocolate Buttercream Frosting (from Southern Living)

Yield: about 4 1/2 cups

1 (4 ounce) white chocolate bar, broken into pieces
1/2 cup whipping cream, divided
1 cup butter, softened
6 cups sifted powdered sugar
2 teaspoons vanilla extract

Microwave chocolate and 1/4 cup cream n a 1 quart microwave-safe bowl at medium (50% power) 1 minute and 10 seconds. Whisk until chocolate melts and mixture [...]