Brew your Vietnamese coffee and set it aside.
Whisk heavy cream and condensed milk over low heat and gradually add pre-brewed coffee.
Turn off the heat and leave the custard cool to room temperature.
Chill it in the fridge overnight or for at least four hours.
Pour the custard into an ice cream maker and turn it on.
Once finished, transfer the ice cream to a clean container, cover it with a lid, and chill in the freezer for four hours.