Add whiskey, cointreau, lemon juice, blackberry puree, 1/2 oz of the vanilla bean simple syrup and half of the ice to a cocktail shaker.
Shake well.
Strain into a lowball glass over the rest of the ice.
In a separate bowl, add the heavy whipping cream and the rest of the vanilla bean simple syrup.
Whip until it becomes a semi-thick cream.
Place a spoon upside down at the very top of the cocktail liquid.
Slowly pour the cream over the back of the spoon. It should sit nicely on top of the cocktail.
Garnish with the blackberry.