Place orange in a large saucepan and pour in cold water to come 1" up sides of pan. Bring to a boil, then remove immediately from heat and drain orange in a mesh sieve or colander. Rinse under cold water; return to saucepan. Add cranberries, sugar, butter, cinnamon, allspice, and salt and bring to a boil, stirring to dissolve sugar.
Cook, stirring often. This is crucial to avoid scorching the cranberries and compromising the flavor. Continue this process until the cranberries burst, and the ingredients become incorporated and syrupy. The whole process should take approximately 12–15 minutes. Once plated garnish with orange zest.
Get a loaf of ciabatta, and save the remaining sauce to make a spectacular Thanksgiving Leftovers Sandwich the next day!