1) Add ice to a large punch bowl. If using chunks (as opposed to a large block of ice), fill the bowl just under half way.
2) Add Cointreau and brandy. Using a ladle or long spoon, stir briefly.
3) Add orange slices and cranberries (if using) and then pour in the champagne.
4) Stir 12 times and let sit for a minute, so the ingredients can get acquainted.