In a medium saucepan over medium heat, warm the cream, milk and 1 cup of the dulce de leche, stirring constantly until the mixture is blended and steam begins to rise from the surface, about 4-5 minutes.
In a large heatproof or metal mixing bowl, whisk together the egg yolks, sugar vanilla, and salt until blended.
Slowly add the hot cream mixture, whisking constantly until fully incorporated.
Transfer the mixture back to the saucepan and set over medium-low heat. Cook without allowing to boil, stirring slowly and continuously with a wooden spoon or spatula, until the mixture thickens to a custard-like consistency, 6-10 minutes, depending on your stove.
Set a fine-mesh sieve over a clean bowl and pour the custard mixture through. Set the bowl in a larger one filled halfway with ice and water and cool the custard to room temperature, stirring occasionally. Refrigerate 1+ hours until chilled.
Transfer the custard mixture to an ice cream maker and freeze according to the manufacturer's instructions. At the end of the freezing stage, add the remaining ½ cup dulce de leche into the churning ice cream until it is swirled throughout.
Transfer the ice cream to a freezable container (like a loaf pan), cover and freeze until firm, 3 to 4 hours.