Start by rinsing the cranberries under cold water and removing any soft or damaged berries. This step ensures clean flavor and the best texture. Drain them well before cooking.
In a medium saucepan, combine sugar and water. Bring the mixture to a boil over medium heat while stirring until the sugar dissolves completely. This creates a sweet syrup that forms the base of the sauce.
Add the cranberries to the boiling syrup. Return to a boil, then reduce the heat and let it simmer. Cook until most of the berries burst and the sauce thickens, about 10 minutes. The natural pectin in cranberries helps it thicken as it cooks.
Remove the saucepan from heat and allow the sauce to cool at room temperature. As it cools, it will continue to thicken. Refrigerate for at least a few hours before serving for the best texture and flavor.