The Champagne Cocktail is one of the great classics of the international IBA recipe book, of course Champagne based.

Champagne Cocktail
¼ oz Brandy
1 tsp Brown Sugar
2 drops Angostura Bitter
Fill Dry Sparkling Wine/Champagne
Build into a Flute glass. You should pour the Angostura Bitter after Brandy and Brown Sugar to support the chemical reaction with the Sparkling Wine, the final ingredient.