To make a mint-flavored simple syrup, begin by boiling the water and sugar with 2 cups of roughly torn and bruised mint in large sauce pot. Boil just until the sugar dissolves completely. Cool and strain the mint out of mixture. Add 2 bottles of whiskey and fruit puree to the infusion. Pour the mixture into a large bottle or pitcher. Stuff the pitcher with the remaining bunch of fresh mint. Cap and put in freezer overnight (if using a pitcher cover with plastic wrap).
Glasses: Wipe the rim of each glass with a lime wedge, then in sugar for a frosted appearance and chill. Fill with julep mixture straight from the frozen bottle and garnish with a mint or lavender sprig.