In a medium bowl, whisk together cold milk, sweetened condensed milk, and instant vanilla pudding mix until smooth and pudding begins to thicken, about 2 minutes.
Refrigerate pudding mixture for 10-15 minutes to set while preparing whipped cream.
In a large bowl, use electric mixer to whip heavy whipping cream until firm peaks form when beaters are lifted.
Gently fold chilled pudding mixture into whipped cream using spatula until no streaks remain, being careful not to deflate cream.
Spread half of pudding mixture into 9x13 inch dish, creating even layer with spatula.
Arrange 3/4 of sliced bananas over pudding layer, then crumble 18 Biscoff cookies and sprinkle evenly over bananas.
Add remaining pudding mixture over cookie layer and spread into even layer.
Top with remaining banana slices and 8 whole Biscoff cookies, arranging attractively for garnish.
Cover and refrigerate for at least 2 hours or overnight before serving to allow cookies to soften and flavors to meld.