Okay, American immigrant to the UK here to explain all the mistakes from Paul Hollywood happening here: there is one fundamentally American ingredient required to make a s'more correctly but which is basically not available anywhere at all in the UK, and that is graham crackers. A plain digestive biscuit close-ish, but still a very different beast.
From Wikipedia: A graham cracker is a sweet flavored cracker made with graham flour.
The next ingredient (which is also extremely traditionally American but slightly more variable) is typically Hershey's chocolate, but you could probably swap this out in the UK with any plain chocolate bar.
Last ingredient is big marshmallows, the kind you do the chubby bunny challenge with, like the size of your thumb and twice as thick.
A proper s'more, the most traditional possible variety, involves to graham cracker squares, two slab segments of Hershey's chocolate, and one to two marshmallows depending on your preference for filling and gooeyness. You put a slab of chocolate on one of the graham cracker squares. Your marshmallows should be toasted, usually over a campfire but if you're doing them at home over a gas stove burner is fine, but the fire part is critical. You can toast them to whatever degree you like, some people like them nice and golden brown but still kind of firm in the middle, me personally? I want that bitch to CATCH ON FIRE, I want it gooey and sticky as hell in the middle, crispy and burnt on the outside. Slap that motherfucker on your graham cracker and chocolate square, top with the other one so your marshmallow and chocolate are sandwiched together by graham cracker on the outside. You do this with your freshly toasted marshmallow because ideally it will be hot enough to start to melt the chocolate so it sticks to the marshmallow and the graham cracker and, combined with the gooey marshmallow, it keeps the whole thing together, and for that reason some people will let them sit for a hot second to let the melting process happen (especially if like me you have chocolate on BOTH graham cracker squares, not just one, because you're a sugar fiend), but if you are a young child you do not have that degree of patience and you eat that shit immediately, unmelted chocolate and all. Consume your summer camp delight like a tiny club sandwich, get gooey sticky marshmallow and chocolate all over your hands, and enjoy.
Important note: this is a kids treat. It is a traditional summer camping trip dessert. It should be something any ten year old with adult supervision and access to the ingredients can make (and make a mess of). They're called s'mores because kids always "want s'more". If you are using a blowtorch, chocolate biscuits, and merengue, you are so far beyond the bounds of s'more-hood that you have thoroughly lost the plot. If you offered Paul Hollywood's concoction to an American child and called it a s'more, they'd tell you flat out that not only is it not a s'more, it looks dumb and you didn't do it right because it's not gooey.