If the wizarding world of Harry Potter (not to be confused with The Wizarding World of Harry Potter at Universal Studios, we're talking about the one in the books) is anything like our world, there is a Starbucks on every corner. Like four in Diagon Alley. A full Starbucks café in the lobby of the Ministry of Magic. And at least one within walking distance of Hogwarts.
And they're about to put that mom and pop shop Hogsmeade out of business: Because Sbux is now unofficially serving butterbeer! We say unofficially because it's part of its "secret menu" of unadvertised drinks.
To order it for yourself, all you have to do is remember this recipe (via DaleBacar.com):
A Crème Frappuccino base, made with whole milk (not skim or 2%, which will mess up the consistency)
3 pumps of caramel syrup
3 pumps of toffee nut syrup
Top with caramel drizzle
There is also a hot alternative to the drink (as there is with the "real" butterbeer):
Whole milk steamer
Caramel syrup (2 pumps for a tall, 3 for grande, 4 for venti)
Toffee nut syrup (2 pumps for a tall, 3 for grande, 4 for venti)
Cinnamon Dolce syrup (2 pumps for a tall, 3 for grande, 4 for venti)
Top with whipped cream and salted caramel bits
Optional: 1 shot of espresso (2 for a grande or venti)
The drink is only available during the Christmas season (aka red cup season), as Starbucks does not carry toffee nut syrup year-round. Food Beast described the drink as "pretty magical and a great festive fall alternative to the Pumpkin Spice."
Non-Potterheads might describe it as "pretty nerdy and HOLY HAGRID! That is way too much sugar for one drink! You are going to get diabetes if you drink that!" To each their own.
Remember: You need to provide the barista with the recipe, as it is not a menu item they are trained to make. If you do not bring the recipe, you do not get the butterbeer. Do not yell at your barista. Do not avada kedavra your barista.