In a medium heavy saucepan, combine 3/4 cup of the dulce de leche, the cream, milk, and sugar. Bring to a gentle boil over medium heat. Remove from the heat.
Beat the egg yolks in a medium bowl. Whisk 1 cup of the hot cream mixture into the egg yolks. Gradually add the egg mixture in a slow, steady stream, to the hot cream. Cook over medium-low heat, stirring occasionally, until the mixture thickens enough to coat the back of a spoon, about 5 minutes. Remove from the heat and strain through a fine mesh strainer into a clean container. Cover with plastic wrap, pressing down against the surface to keep a skin from forming. Refrigerate until well chilled, about 2 hours.
Remove from the refrigerator and pour into the bowl of an ice cream machine. Freeze according to the manufacturer's instructions. When the ice cream is nearly completely thickened, pour in the remaining 1/4 cup dulce de leche to create a swirl in the ice cream. Transfer to an airtight container and freeze until ready to serve.
Yield: about 1 quart