My Mom's Chocolate Sour Cream Frosting

 The birthday cake frosting from my childhood, and still very much enjoyed as an adult. 

Adapted from Debby Kemper

6 oz (170g) unsalted butter, softened
⅔ cup (110g) bittersweet chocolate chips, melted
4 tbsp sour cream
1 ½ tsp vanilla extract
16 oz package powdered sugar

1. In a stand mixer, cream together the butter and melted chocolate chips.

2. Add sugar alternately with the sour cream and vanilla and beat until smooth and fluffy.