Brandy is a complex, flavorful spirit but it can lose some nuance when paired with bold flavors in some cocktails. So when we want to best experience those subtle flavors, we turn to the brandy & soda. Soda lengthens the drink and makes it refreshing, while its bubbles carry scent compounds upward, helping to reveal the woody vanilla notes of a good brandy (or cognac). Its a simple recipe that can barely even be called a cocktail (and by strict definitions, it is not) but it still deserves a place in the drinkers toolbox, for those days when something simple, sophisticated, and refreshing is all you need.