Sour Cream Chocolate Icing

from HTEAC &"Sky High: Irresistible Triple-Layer Cakes."

12 ounces bittersweet or semisweet chocolate, coarsely chopped
1 stick unsalted butter
2 tablespoons light corn syrup
1/4 cup half-and-half, at room temperature
1/2 cup sour cream, at room temperature

Melt chocolate with butter and corn syrup in a double boiler over barely simmering water or in a heavy pan over very low heat. Remove from heat and whisk until smooth. Whisk in half-and-half and sour cream. Use while soft. (If icing is runny, let it cool completely to room temperature.)