01 - Place cranberries, granulated sugar, and water in a medium saucepan. Add the orange peel strip if desired, stirring gently to combine.
02 - Set the saucepan over medium heat and bring to a gentle simmer, stirring occasionally. Continue cooking for 10 to 12 minutes until most of the cranberries have burst and the mixture has thickened noticeably.
03 - Remove from heat. For a smooth, refined syrup, pour the mixture through a fine mesh sieve, pressing down firmly on the berries to extract maximum liquid. Discard the remaining solids.
04 - Stir in the vanilla extract if using. Allow the syrup to cool completely before transferring to a sealed bottle or jar. Refrigerate for up to 2 weeks.