Combine the milk and 1/3 cup of the Vanilla Bourbon Caramel Sauce in a blender and blend until combined. Add the ice cream and blend until smooth.
Drizzle some of the remaining caramel sauce into a glass in a decorative pattern. Pour in the milkshake, top with a dollop of whipped cream, and drizzle with more caramel sauce.
Vanilla Bourbon Caramel Sauce:
Put the cream in a small saucepan, add the vanilla pod and seeds and bring to a simmer. Remove from the heat, cover and let steep while you make the caramel.
Combine the sugar and 1/4 cup cold water in a medium saucepan over medium-high heat; stir to combine. Cook, without stirring, until the sugar has turned a deep amber hue, 10 to 12 minutes.
Remove the vanilla pod from the cream and slowly whisk the warm cream and the bourbon into the caramel. Continue simmering the mixture until smooth, another 2 to 3 minutes. Remove from the heat and whisk in the butter and salt, whisking until smooth. Transfer to a bowl and let cool for 10 minutes.