Place 2 cups of cold vanilla ice cream into the blender.
Pour in 1/2 cup of whole milk (adjust amount for desired thickness).
Add 1/2 teaspoon of vanilla extract to the blender.
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 desired, top with whipped cream, a maraschino cherry, sprinkles, or a drizzle of chocolate syrup and serve at once.