Pour the whole jug of apple cider into a large pot and bring to a boil over medium-high heat.
Reduce the heat to medium-low and simmer or boil gently until reduced to 2 cups. This will take a few hours (3-4).
When about 1 quart of apple cider remains, start measuring the cider periodically as it continues to cook until you reach 2 cups.
Remove from the stove and let sit for a few minutes.
Pour into a heat-safe container and let cool completely.
Store in the fridge.
This will last for months in the fridge.
Use as a flavoring or glaze for meats, vegetables, salad dressings, desserts, etc.