You have come to the perfect place to agree on such matters. First, let us start with a definition of "cake". I consulted the Free Dictionary to find out more about the issue. This is what I found:
cake (keɪk)
n
1. (Cookery) a baked food, usually in loaf or layer form, typically made from a mixture of flour, sugar, and eggs
2. (Cookery) a flat thin mass of bread, esp unleavened bread
3. (Cookery) a shaped mass of dough or other food of similar consistency: a fish cake.
4. a mass, slab, or crust of a solidified or compressed substance, as of soap or ice
5. have one's cake and eat it to enjoy both of two desirable but incompatible alternatives
6. go like hot cakes sell like hot cakes to be sold very quickly or in large quantities
7. piece of cake something that is easily achieved or obtained
8. take the cake to surpass all others, esp in stupidity, folly, etc
9. the whole or total of something that is to be shared or divided: the miners are demanding a larger slice of the cake; that is a fair method of sharing the cake.
vb
10. (tr) to cover with a hard layer; encrust: the hull was caked with salt.
11. to form or be formed into a hardened mass
Judging from the description above, Jaffa cakes indeed qualify as cakes, although we should consider the possibility of multiple interpretations before making hasty judgments.
