1) Add cranberries, orange juice, zest and sugar to a large pan and set over medium heat until berries break down slightly and liquid is syrupy, 12 to 15 mins. Pour into a blender and process, be careful of the hot liquid expanding when you blend - use a towel over the top of the blender. (*see Cook's Note)
2) Strain and discard any solids then set aside and cool.
3) Pour 2 tbsp of cranberry-orange syrup into the bottoms of 4 chilled champagne glasses. Add a few cranberries to each glass and gently top off each glass with Champagne.
* Cook's Note: When blending hot liquids, remove liquid from the heat and allow to cool for at least 5 mins. Transfer liquid to a blender or food processor and fill it no more than halfway. If using a blender, release one corner of the lid. This prevents the vacuum effect that creates heat explosions. Place a towel over the top of the machine, pulse a few times then process on high speed until smooth.