Place the water, cranberries, sugar, and orange zest in a saucepan and bring to a simmer over medium-high heat. Reduce the heat and maintain a simmer until the cranberries have burst, about 7 minutes.
Remove from the heat and stir in the vinegar and molasses. Refrigerate overnight, preferably for 24 hours. Strain out the cranberries and orange zest, pressing the solids in a strainer with a spoon to extract all of the liquid.
Place the frozen cranberries into a large pitcher. Transfer the chilled cranberry liquid to the pitcher and add the orange juice and Campari. Pour in the sparkling beverage of your choice and serve chilled.
Notes
Remember to freeze 2 cups of cranberries ahead of time.
Make sure to allow enough time for the base of the shrub to chill.
You might garnish the glasses with a wedge or wheel of fresh orange, or add a sprig of fresh rosemary to each glass.
Leave out the Campari if you are making a shrub mocktail. And if you are making both mocktails and cocktails, think about serving them in different types of glasses so they don't get mixed up.