Which ingredient adds a sweet note to the Brandy Alexander?

In a Brandy Alexander, dark crème de cacao is the ingredient that adds a sweet note and contributes to the cocktail's rich, chocolatey flavor. The liqueur is made from cacao beans and is sweetened, providing both sweetness and depth to the drink. This addition complements the brandy and cream, creating a harmonious blend that is characteristic of this classic cocktail.

While ginger ale, white sugar, and soda water can add sweetness or flavor, they do not provide the specific chocolate notes that dark crème de cacao brings. Ginger ale is typically carbonated and would add a different kind of sweetness and flavor profile, while soda water would dilute the drink without adding sweetness. White sugar could enhance sweetness but is not traditionally used in a Brandy Alexander, which specifically calls for crème de cacao for that unique flavor combination.