Cream butter in a large mixing bowl; gradually add sugar, beating well. Stir in whipping cream and vanilla. Chill mixture overnight. Shape into 3-inch eggs. Chill until firm.
Place chocolate in top of a double boiler; cook over simmering water, stirring until chocolate melts. Remove from heat, leaving chocolate over hot water. Using 2 forks, quickly dip eggs, one at a time, into chocolate mixture. Place on waxed paper-lined baking sheets; refrigerate until firm. Decorate with Royal Frosting, as desired. Store in airtight containers in refrigerator.
Note: Shape mixture into 1-inch eggs to make 2 dozen.