Banana Cake Fail

I'd love to know if anyone else has tried the 'no fail' banana cake from Kirstie Allsop's most recent book 'Craft'. I wouldn't say I'm an expert by any means but I can generally make cakes ok. But somehow, I managed to get this apparently super reliable cake to flop.

Abandon ship! We're sinking!

When I put it in the oven, it had a sort of 'souffle' type texture to it which was fine - my favourite pudding has the same type of texture and that comes out great (ok, now I'm wanting to make that...yum yum yum) but as soon as this came out  it just started sinking and didn't stop! Despite being a recipe for a 2lb loaf tin, four bananas are called for. This seemed quite a lot, and more than other banana cake recipes I've used (which have all worked) call for. I do wonder if it's a bit much for that size cake.

Either way, I can't say it's something I'll be trying again. I'll stick to previous ones I've made that I know work but I'd love to hear if anyone else has had success with this recipe or if it's just me.