This recipe for apple butter is from Chef Paul Fehribach's cookbook Midwestern Food. In this book, you can find many more recipes and a lot of history of Midwestern food and culture.
You can preorder this cookbook now.
Pour the apple cider into a 4-quart or larger nonreactive pot, bring to a boil, and reduce by half. Add the apples, orange zest, sugar, acids, spices, and salt, and stir to coat the apples. Reduce heat to medium low and render the apples, stirring occasionally with a wooden spoon so they cook evenly. When they are thoroughly softened and mushy, in about 1 hour, remove from heat and puree in the blender or food processor.
Preheat oven to 275°F.
Transfer the puree to an enamel or glass roasting pan and place on center rack of the oven, uncovered. Use a rubber spatula to stir the butter and scrape down the sides of the pan as it cooks and reduces, every 20 to 30 minutes. Cook for 4 to 6 hours, until you can stand a small spoon in the butter.
Transfer to sanitized canning jars or bottles while hot and cap tightly with new lids. Apple butter can be refrigerated indefinitely or canned in a standard water bath to store in the pantry.