In a medium saucepan, whisk together the milk, heavy cream, sugar, cornstarch, and salt.
Cook over medium heat, stirring constantly until the mixture thickens and begins to bubble, about 5-7 minutes.
Remove from heat and stir in the vanilla extract.
In a 9x9-inch baking dish, layer half of the crushed Biscoff cookies on the bottom.
Add a layer of sliced bananas on top of the cookies, followed by half of the pudding mixture.
Drizzle half of the caramel sauce over the pudding.
Repeat the layers with the remaining Biscoff cookies, bananas, pudding, and caramel sauce.
Cover the dish with plastic wrap and refrigerate for at least 4 hours, or overnight for best results.
Before serving, top with whipped cream and additional crushed Biscoff cookies if desired.