1. Take four tall glasses and lightly spoon or squeeze the sauce into stripes down the inside of the glass.
2. Carefully pour in milk so glass is 2/3 full and top with ice cream.
3. Serve with a straw. You could decorate with chocolate sprinkles.

Cook's tip: Using a commercial chocolate topping – the type that hardens – is important here, as it will quickly set to form the stripes.