Adapted from 1968 Better Homes & Gardens Cookbook "Sour Cream Frosting",
page 86:

6 oz. chocolate chips
1/4 cup (1/2 stick) butter
1/2 cup sour cream
1 tsp. vanilla
1 pinch salt
at least one box of confectioners' sugar

Melt butter, then add chocolate chips.
Blend in sour cream, vanilla, and salt.
Add confectioners' sugar until proper consistency.