Reduce the 1½ liters of root beer down to 2 cups in a medium saucepan over medium heat. This should take about an hour, so pull up a chair and a good book.
In a medium saucepan over medium heat, mix together the sugar, milk, and light corn syrup. Heat, stirring often, until right before it boils. Remove from heat.
Add the reduced 2 cups of root beer, 1 cup of unreduced root beer, and 1 teaspoon vanilla extract to the milk mixture and stir to combine.
Cover and chill in the refrigerator for about 8 hours.
Follow the directions on your ice cream maker to mix the batter into ice cream, until it reaches the desired consistency. This is the conversion process.
Freeze for another 2 to 4 hours while the ice cream hardens and ripens. Note: if you taste the ice cream before you ripen it in the freezer, it will taste very sweet. This sweetness subdues after freezing.
This nutritional information has been automatically calculated, and as such, may be incomplete or inaccurate. Please reference the specific ingredients you use for the most accurate nutritional information.