Sour Cream Fudge Frosting

Sour Cream Fudge Frosting
16 oz. high-quality milk chocolate (such as Lindt. *Apparently there is a difference in flavor between American and European styles of chocolate. I used a mix of Lindt and Ghiradelli, mostly Lindt.)
1 stick unsalted butter at room temperature
1 and 1/3 c. sour cream
8 tsp. light corn syrup
Place chocolate in large metal bowl. Set bowl over saucepan of simmering water and stir until melted and smooth. Remove bowl from over water. Add butter and stir until melted, then add sour cream and corn syrup and whisk until smooth. Let frosting stand at room temperature until thick enough to spread, about 20 minutes.
(There was a cake batter to go with this, but honestly, I think a boxed devil’s food cake would have been just fine. It’s really the frosting that makes it. I made 3 layers--only 2 layers with a boxed cake--and pushed toasted hazelnuts onto the sides.)