Scaling up for retail bakeries is simply multiplying recipe ingredients. But when factory equipment is used, then the balance changes. Don't want to fight with anyone. This is my experience. The area of the 18 cm diameter pan is 254 cm squared (see nice calculation above).
This issue increases exponentially if you live in a household of just one or two. But that doesn't mean you need to go down a rabbit hole of mug cakesfor one. It just means you should get to know your recipes and how to scale them down. However, that's not as easy as you might think.
Unfortunately we haven't tried scaling up any of Nigella's cakes so we aren't able to offer any specific advice on the scaling up of her cake recipes. Scaling up cake recipes is also tricky at times as the larger a cake becomes, the more difficult it is to make sure that the cake bakes all of the way through without burning on the outside.
It just means you should get to know your recipes and how to scale them down. However, that's not as easy as you might think. With savory cooking, scaling down usually means simply cutting a recipe in half. But the science of baking makes this risky.