In a small bowl, combine about ¾ cup of milk with the cornstarch, vanilla and salt. Whisk until smooth and set aside. In a large saucepan, combine the 1 cup of the sugar with the water and bring to a boil over medium/high heat. Cook, without stirring until a deep amber caramel forms, anywhere from 7-8 minutes. Be sure to watch the mixture, as caramel has a tendency to go from gorgeous amber to burnt as hell. Once the mixture reaches the desired amber hue, remove from heat and gradually whisk in the remaining 3 ¼ cups of milk. Don’t worry if your caramel changes color. This is normal. Add the remaining ½ cup of granulated sugar and return the pot to the stove. Whisk the mixture over medium/high heat until the caramel and sugar have dissolved. Reduce the heat to low and simmer, stirring occasionally until the mixture thickens a bit and deepens in color, about 10 minutes or so. Gradually add the cornstarch mixture into the caramel, whisking vigorously until the pudding thickens. This can take anywhere from one minute to at most, five. Strain the pudding over a fine mesh strainer set over a large measuring cup with a lip. Pour or scrape the pudding into 8, 4 ounce ramekins and place in the refrigerator to set, about two hours. As the pudding sets, make the Biscoff crumble and cookie butter whipped cream.  

In a bowl of an electric mixer fitted with a whisk attachment add half the whipped cream and beat on high speed until very slightly thickened. Lower the speed to medium and add the cookie butter. Add the rest of the whipped cream and confectioners’ sugar and whip over high speed until medium to stiff peaks form, about a minute and a half or so. Be careful not to over whip or the mixture will curdle and you would have wasted half a cup of cookie butter. Remove from mixer and transfer to a pastry bag fitted with a round or star tip. Place whipped cream in the refrigerator to cool while the pudding sets.

Heat the oven to 325° Fahrenheit. Line a rimmed baking sheet with parchment paper and set aside. Place the Biscoff cookies in Ziploc back. Using a rolling pin or your hands, crush the cookies until they’re coarsely ground. Transfer them to a small bowl and stir in the sugar, cinnamon, and salt. Add the melted butter and use a spoon to evenly combine the butter into the crushed wafers. The mixture should appear slightly moistened. Transfer the mixture to the prepared baking sheet, spreading slightly with an offset spatula. Toast in the oven until brown and fragrant, about 10 minutes. Remove from the oven and set aside to cool. (The crumbs can be stored in an airtight container for up to 5 days at room temperature). To serve: Remove pudding and whipped cream from the refrigerator. Pipe or spoon whipped cream over the caramel pudding. Top with Biscoff crumble and serve.