Take 1 tablespoon of Biscoff spread and smear it around the outside rim of the glass, covering about 1-2 inches.
Place the crushed Biscoff cookie crumbs on a flat plate, then dip the coated rim into the crumbs so they stick evenly.
Optionally, use a teaspoon to create streaks of Biscoff spread inside the glass for a decorative caramel design.
Save any remaining cookie crumbs for sprinkling on top or use a whole Biscoff cookie for garnish later.
In a blender, add 1 heaped tablespoon of Biscoff spread, 3/4 cup of milk (or plant-based milk), and 3-4 scoops of vanilla ice cream (or vegan ice cream).
Blend on medium to high speed until smooth and creamy; if it’s too thick, add more milk until the consistency is just right.
Carefully pour the milkshake into the decorated glass, making sure not to disturb the crumb rim or the streaks of Biscoff inside.
Add whipped cream on top (for vegan version, use coconut whipped cream), sprinkle with cookie crumbs, or crumble a Biscoff cookie over the milkshake.
Finish by placing a whole Biscoff cookie on the side or drizzle some melted Biscoff spread for an extra caramel touch.