Burger Boi is a British fast-casual concept built on two things it does properly: smash burgers with a crust seared on a screaming-hot flat-top, and chicken marinated in buttermilk and fried until crisp. It bets on a tight, sharply focused menu and a young, bold brand that speaks the language of social media and city culture. It differs from ordinary fast food in that, instead of an endless menu, it leans on a handful of items executed without losing quality — fewer options, but each one lands.