Grease and line the pan (Triple lining is suggested to prevent scorching).
Take a LARGE mixing bowl, cream the butter and sugar. Then add the eggs, one at a time to prevent curdling (you may need to add a little flour from time to time). Once the eggs are mixed in, fold in the balance of the flour.
Cook for 30 minutes at 180 deg. then cover with baking parchment for another 20 minutes at the same temperature. For the final 15 minutes, keep covered but reduce the temperature to 170 deg. (Gas 3).
This should produce a cake that has a close, even texture, is completely cooked and moist.
To adapt for chocolate cake: (with thanks to Lorna Shannon)
Substitute 3 desert spoons of good cocoa powder for 3 desert spoons of flour. Then add a further 2 heaped desert spoons of cocoa powder. You can substitute 200gm of the butter for Flora to make it lighter. This should result in a bouncy, good textured chocolate sponge.
If you use more than one cake mix as the pan is big be careful it cooks all the way through. When I have done this I have turned the oven lower than the recipe states and put tin foil over the top to stop it burning. You needto ccheck it quite often though.
SmallBoy turns four at the end of the month and we've been discussing his cake. He originally requested a "line cake" which, when talking about it, was a cake with train tracks across it. I thought I'd get one of those Lakeland sphere pans and make a hill with tracks going over it and put on train candles. We got to Lakeland and they didn't have the big one AND SB insisted he didn't want a hill but a square cake. So, not having any square pans, I bought a big one (to fit the trains on).
Since getting it home I have realized the pan is massive -- 30 in. . Still doable and will definitely feed everyone. But I've never made such a large cake before.
Do I just double one of existing recipes? Are there recipes out there for such large cakes? My oven is on the fritz at the moment so am making the cake at my MiL house so I don't have the ability to play around to get it right.