For example, Marmite Crumpets don’t exist. You cannot buy them at the supermarket. To be clear: you can buy crumpets, you can buy marmite, you can buy butter; but you have to assemble them at home.
If you walk into a breakfast cafe, they will happily serve you sausage / egg / bacon / french toast / bubble / squeak (whatever that is). But no marmite crumpets. If you ask them to make it, they will give you a very strange look. It’s not typically offered. It’s something you just have to make at home.
It is unbuyable. Any tourist who comes to the UK to try a Marmite crumpet would need to bring a toaster or an oven with them, or quickly befriend a brit and hope that they have all the ingredients at home.
It’s not a secret. You just can’t have it.
*munches into crumpet thoughtfully, and salivates at the juicy savory delight, whilst staring at you pityingly and condescendingly*
Anyway, what’s something that I could never experience unless I made it myself in your local?
Eey, I make apple butter! It’s great. I do know some places you can buy it though…roadside stands! Farmer stalls or markets. Though those may be more common here, being the garden state. Still better making it at home, get to pick the apples and how much you let it cook down!