01 - Place cranberries, sugar, and water in a medium saucepan. Add the orange peel if using.
02 - Bring to a simmer over medium heat. Stir occasionally and cook for 10 to 12 minutes until most berries burst and the sauce thickens.
03 - Remove from heat. For a smooth syrup, strain through a fine mesh sieve, pressing the berries to extract all liquid. Discard the solids.
04 - Stir in vanilla extract if using. Let cool completely. Transfer to a sealed bottle or jar and refrigerate for up to 2 weeks.