In a saucepan over medium heat, combine the milk, 1 1/2 cups of the heavy cream, salt, and half the sugar. Stir the mixture constantly as you bring it just to a simmer (do not boil). Once steaming, remove from heat.
In a small bowl, whisk together the egg yolks and remaining sugar just until combined.
To temper the eggs, slowly add 1/2 cup of the milk mixture in a drizzle into the egg mixture. Do this slowly so as not to cook the eggs.
Pour the entire egg mixture back into the saucepan with the milk mixture. Simmer over medium heat, stirring constantly, until slightly thickened, about 5 minutes. Do not boil.
Remove the pot from the heat. Strain it through a fine mesh sieve into a bowl and let cool.
Once cooled, divide the mixture into two bowls. Pour the remaining 1/2 cup heavy cream and vanilla into one bowl to make the vanilla base. Pour the orange zest and orange juice into the other bowl to make the orange base.
Refrigerate both for at least two hours until cold.
You will churn each base mixture separately, so pour the vanilla base into the ice cream maker and churn for 15 minutes. Transfer the vanilla ice cream to one side of a freezer safe container and freeze.
Next pour the orange base into the ice cream maker (no need to refreeze or wash in between). Churn until the ice cream is thick, about 15-20 minutes. Transfer the orange ice cream to the other side of the freezer container. You can swirl them together slightly, if desired.
Freeze the ice cream for at least 3 hours to set before serving.