Melt the candy bars and condensed milk in a heatproof bowl set over a saucepan of simmering water, stirring, until smooth (do not let the bowl touch the water). Remove the bowl from the saucepan and whisk in the milk, half-and-half and chocolate syrup. Refrigerate until cold, at least 2 hours.
Churn the mixture in an ice cream maker. Transfer to an airtight container and freeze until firm, at least 2 hours. Photograph by Antonis Achilleos