Another Chocolate Frosting

The was found on recipegirl.com

CHOCOLATE BUTTERCREAM FROSTING:
(double this recipe if you want to pipe the frosting)
1/2 cup salted butter, at room temperature
3 ounces cream cheese, at room temperature
1 pound powdered sugar, sifted
1/4 cup milk
1 teaspoon vanilla extract
1 cup dark chocolate chips (or chopped dark chocolate)

Directions:
In a large bowl, use an electric mixer to beat the butter and cream cheese at medium speed until creamy. Gradually add the powdered sugar, beating at low speed until blended. Increase speed to medium, and slowly add milk and vanilla, beating until smooth.

Microwave the chocolate chips in a microwave-safe bowl at MEDIUM 1 1/2 to 2 minutes or until melted and smooth, stirring at 30 second intervals. Gradually add melted chocolate to mixture; beat until blended and smooth. If the frosting is too soft for piping, cover and refrigerate for a few minutes until it firms up a little bit. Otherwise, spread frosting on top of cupcakes and decorate as desired.