There are two big ambiguities here: what counts as a cake, and what counts as using sugar? On the first one, there are sweet (cheesecake) and savoury (oatcake) baked goods which have "cake" in their name but which I wouldn't strictly classify as cakes. On the second one, is the restriction really "no processed sucrose", so that e.g. processed fructose or mashed apple would be allowed as substitutes? What about unprocessed or partially processed sucrose, such as molasses? Glucose? Honey?

@PeterTaylor As to how to define a cake, I thought about anything that's sweet, has to be baked and needs flour. Cheesecake is more like a tart (but I guess that it could sill count as cake somewhere...) while oatcakes are crackers. For the sugar part, it may be better to put up the condition to not use refined sugars (so nothing that is processed in any way)? This would allow to use fruits and honey as substitutes.

I'm not sure whether you disagree with me on the meaning of oatcakes, crackers, or both, but I think there's a dialectal minefield here :( For me, oatcakes have a soft inside (they're not entirely dissimilar to scones or dumplings) whereas crackers are thin and snap all the way through. Refined isn't quite the same as processed: most honey is processed, but I don't think it's refined. Maybe "no white crystals" would work (although it does allow demerara sugar)?

What if you broadened the challenge to a dessert? That avoids the ambiguity in defining a cake. I would define a dessert as a sweet food eaten as the course concluding a meal.

@PeterTaylor Probably less a dialectal than a translation problem: I didn't know about oatcakes beforehand and translated it into my mother tongue and it came out as something that's related to biscuits / cookies. Recipes in my language show it as something more orientated towards cookies / crackers with a hard inside, hence I wrote it. I like the idea with no white crystals, perhaps extend it for brown crystals as well?

@Sigma Don't you think that broadening the scope to a dessert might make it a bit too broad? I thought about it too but submitted posts might vary a lot making it hard to really compare them (which may also be a no-issue).

That could be a concern but since it's not a contest I'm not sure it would matter. Maybe add a condition that it needs to be baked? That way you get cakes, pies, cookies, tarts, and scones, but a fruit plate won't be included.

@Sigma The condition about baking sounds like a reasonable thing to do.