Roughly chop the biscoff biscuits on a chopping board and place them to the side. Add whole milk to a large blender.
Add vanilla ice cream and biscoff spread, and starting the blender on slow, slowly work your way up to medium, blending for 30 to 40 seconds until smooth and pourable.
Next add 90% of the roughly chopped biscuits and mix with a tablespoon.
Pulse the milkshake 4 to 6 times until incorporated. If you like biscuit chunks in your milkshake, make sure to not over pulse. Serve in a cool glass with two thicks straws, and a sprinkle of the leftover crushed biscuits.