Makes 6 drinks.
In a small bowl combine the mint leaves and the bourbon, crushing the mint slightly to extract the flavor, and chill the mixture, covered, for at least 6 hours or overnight. (The flavor improves the longer the mixture is chilled.) Strain the bourbon mixture
through a fine sieve into a bowl, pressing hard on the mint leaves, and discard the leaves. Spoon 2 teaspoons of the bourbon into each of 6 champagne flutes, divide the champagne among the flutes, and garnish the drinks with the mint sprigs.