STIR vanilla liqueur and bitters with two ice cubes in a glass. Add half the bourbon and two more ice cubes. Stir some more and add another two ice cubes and the rest of the bourbon. Add the last two ingredients and more ice cubes and stir lots more. The melting and stirring of the ice cubes is essential to the dilution and taste of the drink.
Lemon zest twist
Tames bourbon and adds hints of apricot, vanilla and apple.