In 1-quart saucepan, heat chocolate chips and shortening over low heat, stirring constantly, until chocolate is melted and mixture is smooth; remove from heat. Using 2 forks, dip and roll chocolate balls, one at a time, into melted chocolate; tap off excess chocolate. Place on lined cookie sheet. Immediately sprinkle with nuts. If chocolate has cooled too much, reheat. Repeat with remaining chocolate balls.