01 - Place cranberries, sugar, and water in a medium saucepan. Add the orange peel if desired, then stir to combine.
02 - Set the saucepan over medium heat and bring to a simmer, stirring occasionally. Cook for 10 to 12 minutes until most of the berries have burst and the mixture thickens.
03 - Remove from heat. For a smooth syrup, press the mixture through a fine mesh sieve using the back of a spoon, extracting as much liquid as possible. Discard the solids.
04 - Stir in the vanilla extract if using. Allow the syrup to cool completely, then transfer to a sealed bottle or jar. Refrigerate for up to 2 weeks.