For the punch: Add the maple syrup and rosemary to a small pot. Let steep over LOW heat for 20 minutes, WATCH IT CLOSELY! Even over low heat, it can easily boil over and make a sticky mess. Allow to cool.
Once cool, remove the rosemary and pour the maple syrup into a pitcher. Add the apple cider, bourbon and lemon juice. Whisk to combine.
To serve: Serve punch over ice with rosemary stalks and apple slices as garnish.