Melt the chocolate chips over low heat in a double boiler.
Remove them from the heat and blend in the sour cream. Refrigerate the mixture overnight.
The next day combine the wafer crumbs with the butter, cocoa, icing sugar, rum and nuts. Mix them together well. Form the chilled chocolate mixture into tiny balls and roll them, first in the crumb mixture, then in the chocolate sprinkles or coconut.
Store in an airtight container in the refrigerator for 24 hours to allow the flavors to meld before eating. This rum ball recipe makes 3 dozen balls.