In a large mixing bowl, whisk together the brown sugar and milk until the sugar dissolves., Blend in the heavy cream, then whisk in the eggs, cinnamon, cinnamon oil, and salt. The cinnamon oil is the key to the warm, spicy flavor of this ice cream; we don't recommend leaving it out., Chill this base in the refrigerator for 2 to 3 hours, or up to overnight. A cold base will freeze faster, making for a creamier ice cream in the end. If your ice cream maker has a removable bowl that needs to chill in the freezer, make sure it's fully chilled before using., Freeze in your ice cream machine according to the manufacturer's directions.