In a medium bowl, whisk together the egg yolks, sugar and salt. In a medium saucepan, heat the cream and buttermilk over medium heat, stirring occasionally, until almost simmering, about 5 minutes. Add to the egg mixture in a slow stream, whisking constantly, then pour into the saucepan. Cook over medium-low heat, stirring constantly, until the custard thickens and registers 175 degrees on an instant-read thermometer, about 8 minutes.
Pour the custard into a medium bowl set in an ice water bath; stir in the vanilla. Let cool, then cover and refrigerate for at least 4 hours.
Using an ice cream machine, process the custard according to the manufacturers instructions. Fold in the chopped candy bars, then transfer to an airtight container and freeze until firm, about 4 hours.
