In a medium bowl, whisk together cold milk, condensed milk, and vanilla pudding mix until the pudding mix has dissolved. Set aside in the fridge to set while you make the whipped cream.
In a large mixing bowl, add whipping cream. Use an electric hand mixer fitted with a whisk attachment to whip the cream until it becomes firm peaks.
Add the chilled pudding mixture to the whipped cream and fold them together with a spatula until no streaks remain.
Add half of this pudding mixture to a 9x13" dish. Use a spatula to spread it into an even layer.
Slice the bananas into ¼" thick coins and add about ¾ of them on top of the pudding layer. Crumble up about 18 biscoff cookies and sprinkle them on top of the banana layer.
Add the rest of the pudding mixture on top and spread it out into an even layer.
Repeat adding the rest of the biscoff cookies and banana slices on top as garnish. If you want to serve your banana pudding in the dish 1-2 days later, slice and add the last banana on top right before serving to prevent them from turning brown.
Cover and chill the biscoff banana pudding in the fridge for at least 2 hours or overnight before serving. Serve by scooping directly from the dish or divide into smaller containers if you prefer it to be mixed.