My thought is that it will be very sweet—adding sugar to chocolate, you know? Plus, unless all the sugar is dissolved, it might get gritty.
You could just make a sour cream ganache—which is amazingly delicious! Rose has a recipe in TCB, for sure, and probably in RHC, too (can’t remember offhand). It’s only chocolate and sour cream and it is HEAVENLY!
Her milk chocolate frosting is also incredible and incredibly simple—it’s in TCB. It’s just melted chocolate and butter. It tastes like a soft milk chocolate bar. It is truly to die for—just don’t refrigerate it. It’s soft as a happy whippy dip, but if you refrigerate it, it’s hard as .... cold chocolate mixed with butter! Melts in your mouth beautifully, but it’s no longer like frosting.