Chocolate Sour Cream Frosting

This is my mom's recipe that we grew up using.  Sometimes I get a craving for this frosting.  It's super yummy!

1/2 c. butter softened
9 TBL. cocoa
3 c. powdered sugar
1/2 c. sour cream

Mix all ingredients together with a hand mixer and use on brownies, cakes, cupcakes.