For the base:
Put all of the ingredients in a bowl and mix well with a balloon whisk. Pour this mix over the biscuit base and then (carefully) return to the oven for another 20 minutes, until the topping has set.
Once baked, remove, allow to cool in the tin and then place in the fridge overnight so it sets completely (will make slicing easier). Dust with icing sugar if the whim takes you.
I haven't baked this for me, but I couldn't send an untested pan of zesty yum to any of my acquaintances in good conscience, which is why an end of this is missing.
Quality control approved.
I forgot to tap the pan on the countertop before I put it in the oven, which is why I think there are bubble marks on the surface. Still doesn't distract from the taste and nothing that a little icing sugar won't distract from.