In a small saucepan, add the cranberries, orange zest, and water and place it over medium heat. Bring to a boil. Once it starts to boil, reduce the heat and let the mixture simmer for 5-6 minutes, or until the cranberries have popped.
Remove saucepan from the heat and let it cool for 5 minutes. Stir through the allulose then let the sauce cool completely.
Once cool, transfer into a sterilized jar or sealable container.
Notes
Sweetener: I don't recommend erythritol or monk fruit sweetener, as it doesn't dissolve as nicely as sugar.
Leftovers: Keep in the fridge for up to two weeks or the freezer for up to 6 months.