01 - Place the cranberries, granulated sugar, and water into a medium saucepan. Drop in the orange peel if using, and stir to combine.
02 - Set the saucepan over medium heat and bring to a gentle simmer, stirring occasionally with a wooden spoon. Cook for 10 to 12 minutes until most of the cranberries have burst and the mixture has thickened into a sauce-like consistency.
03 - Remove the saucepan from heat. Pour the mixture through a fine mesh sieve set over a bowl, pressing down firmly on the berries with the back of a spoon to extract all the liquid. Discard the solids and peel.
04 - Stir in the vanilla extract if using. Allow the syrup to cool completely, then transfer to a clean sealed bottle or jar. Refrigerate for up to 2 weeks.