In heavy guage saucepan, combine 1 1/4 cups heavy cream, milk, sugar and 1 cup of mint chocolate chips. Cook over low heat, stirring with wire whisk, until chips are melted and mixture is smooth. Remove from heat. In a medium bowl, beat egg yolks and salt until thick. Gradually add chocolate mixture, beat until well blended. Chill 30 minutes. In a small heavy guage saucepan, combine remaining 1/2 cup of chips and 1/4 cup of heavy cream. Cook over low heat, stirring constantly, until chips are melted and mixture is smooth. Remove from heat and set aside. Pour chilled chocolate/egg mixture into an electric iceream freezer; churn until thick, about 25 minutes. Pour in reserved chocolate mixture; churn 10 seconds more. Remove dahser; cover and store in freeze until ready to serve.