Melt the chocolate in a double boiler or the microwave. Stir the chocolate until smooth. Set aside.
Add the butter into a mixing bowl and beat at medium speed until smooth and pale. Mix in the vanilla. Gradually add the powdered sugar and salt until smooth.
Continue to mix at low speed to fold the sour cream into the cool melted chocolate.
Store in an airtight container in the refrigerator until ready to frost.
Notes
If you stored the Creamy Sour Cream Chocolate Frosting in the refrigerator before frosting or filling, mix at medium speed to soften for spreading. Sour cream frosting should be kept cool. Store chocolate sour cream frosting in the refrigerator up to five days.