Rinse fresh cranberries under cold water, removing soft or bruised ones. In a saucepan, combine cranberries and water. Cook for 5 minutes until they start to burst.

Add brown sugar to the bubbling cranberries. Stir until dissolved, then cook for another 5-7 minutes until the sauce thickens.

Sprinkle in cinnamon and nutmeg, then add orange zest. Simmer for another 3-5 minutes.

In a separate saucepan, melt butter and stir in dark rum. Cook for 1-2 minutes.

Combine the hot buttered rum mixture with the cranberry sauce and stir well. Simmer for an additional 2-3 minutes.

Cool to room temperature, then transfer to an airtight container and refrigerate for at least 2 hours or overnight.

To reheat, warm in a saucepan over low heat for about 5 minutes, adding water if too thick.