TikToker @ellbrxo posted a video for the 'McDonald's hack', writing: "Thank us later."
In the clip, she removes the lid from a McDonald's milkshake so that a warm espresso can be poured in. A quick stir later, and the drink is ready to go.
Talking us through the directions - just in case you didn't quite get the premise - she says: "This is vanilla milkshake from McDonald's and an espresso shot - you whack it in, and then you mix it.
"The smell of that, smells like Costa!"
She continues: "Then you start mixing together. When you have a normal McDonald's milkshake anyway it's well lumpy, but this makes it a bit more juicy.
"And then voila! Frappuccino thing!"
The video has racked up more than 28,000 likes and 274,000 views, with many commenting to say they'd be giving it a go.
One wrote: "This is the best video I've seen today."
Another said: "Why have I never thought of this?"
Tagging a friend, someone else said: "We need to try this."
Others said they'd also tried the trick before using other flavours, including chocolate and banana.
If you want to try if for yourself, simply head down to your local McDonald's and order a milkshake (£1.69 for regular; £1.99 for large) and a double espresso (99p), and you're good to go.
The idea's been floating around on the internet for some time now, although it's hard to know who came up with it first.
It's basically a riff on the classic Italian dessert affogato, which sees warm espresso poured over ice cream so that it melts slowly.
Food writer and chef Elly Curshen, who's known on Instagram as @ellypear, has been doing it for years now with her McDonald's milkshakes, having built something of a cult following for the drink after sharing the hack on her feed.
Sharing a variation with chocolate milkshake in 2018, Curshen referred to it as 'the best #mcdonaldshack of them all'.
A group of police officers also went viral later that year for the same hack, following a tip-off from Twitter account @UKCopHumour, with McDonald's saying at the time it would be offering the drink to officers on duty free of charge.
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