If desired, rim a rocks glass with sugar. Muddle cranberries in glass. Add rye whiskey, bitters and cranberry simple syrup. Add ice and stir well. Garnish with cranberries and an orange peel.
Cranberry Simple Syrup
1 cup sugar
1 cup water
Combine cranberries, sugar and water in a sauce pan over medium-high heat. Bring to a boil. Stir regularly until cranberries begin to break down and release juices and sugar is dissolved. Remove from heat. Allow to cool. Strain cranberries out of solution and discard. Transfer simple syrup to an airtight container. This will keep in the fridge for about 2 weeks.