In small saucepan, bring cream and butter to a boil. Remove pan from heat. Add chocolates and vanilla and whisk until mixture is creamy and smooth. Refrigerate about 2 1/2 to hours, until firm enough to handle.
Form into 1" balls8*, then roll in cashews.
Store in refrigerator.
*Note: It's easiest to take a teaspoonful of chocolate and roll it right into balls in the chopped nuts rather than try to make a nice ball before rolling.