Pour the cider into a large, enameled cast-iron Dutch oven or nonreactive stockpot. Bring to a boil over medium-high heat. Reduce the heat to low and cook, stirring occasionally, until the cider thickens and reduces to about 2 cups, about 5 hours.
Transfer into a glass jar, cool, cover, and refrigerate for up to 3 months.
Note: When stored in a sterilized jar, boiled cider keeps for a year or more in the refrigerator and can be enjoyed in myriad ways. Drizzle it over pancakes, cornbread, ice cream, or oatmeal; stir it into cocktails, other beverages, vinaigrettes, and sauces; add it to a cheese plate; use it in baked goods; spoon it over sweet potatoes, winter squash, and baked beans…you get the idea. In short, use boiled cider wherever you need a solid dose of intense apple flavor.