Divide the Champagne evenly between 2 Champagne flutes. Slowly add the creme de cassis so that it settles at the bottom of each glass. Serve immediately.
Cook's Note: when prepared in this manner the creme de cassis will form a pink layer at the bottom of the glass. If you wish a more uniform cocktail, add the creme de cassis first to the glasses and then add the Champagne.