To build a Champagne tower, arrange 16 Champagne coupe glasses in even rows, 4-by-4, with all glasses touching. Pour 1 ounce creme de cassis into each glass.
Place 9 glasses in even rows, 3-by-3, on top, with all glasses touching, then pour 1 ounce creme de cassis into each glass. Build 4 glasses on top in rows, 2-by-2, in the center, again filling each with 1 ounce creme de cassis. Place 1 glass at the top of the tower, also in the center, and fill with 1 ounce creme de cassis.
Slowly pour Champagne into the top glass and let it overflow into the glasses below, continuing to pour until all the glasses are full. Top with black currents or black raspberries and serve.