Crush your biscuits: Place 120g of chocolate sandwich biscuits in a sturdy zip-lock bag and bash them with a rolling pin until you have a mix of fine crumbs and pea-sized chunks. You want to hear a distinct crackling sound as the biscuits break—stop when you see a variety of textures, from sandy powder to little nuggets.

Soften the ice cream: Scoop 500ml of full-fat vanilla ice cream into your blender jug and let it sit for 2 minutes. It should look slightly glossy around the edges and feel soft when you press the back of a spoon through it, but still hold its shape.

Add the liquid: Pour in 200ml of whole milk, ½ teaspoon vanilla extract, and 1 tablespoon caster sugar if you like it sweeter. Swirl the jug gently to combine—the mixture should look pale and creamy, with a faint vanilla aroma rising up.

Blend the base: Pulse the blender 3 or 4 times, each pulse lasting about 2 seconds. You are not trying to make a smoothie; you just want the ice cream and milk to marry together. The mixture should look thick and homogenous, with a consistency similar to pourable custard.

Fold in the biscuits: Tip in three-quarters of your crushed biscuits and stir them through with a long spoon. Do not blend again—you want those chunks to stay intact, giving you a satisfying crunch with every sip.

Pour and garnish: Divide the milkshake between four tall glasses. Top each with a generous dollop of lightly whipped double cream, a sprinkle of the reserved biscuit crumbs, and a maraschino cherry if you are using them. Serve immediately with a thick straw.