Place 480ml good-quality vanilla ice cream into a blender.
Pour in 120ml whole milk, adjusting the amount for your preferred thickness.
Add 2.5ml vanilla extract.
Secure the lid and blend on high until completely smooth, stopping to scrape down the sides if needed.
Immediately pour the milkshake into a tall glass.
If you like, top with whipped cream, a maraschino cherry, sprinkles or a drizzle of chocolate syrup, then serve straight away.