Key Lime Pie

I suppose outside of the States, possibly even Florida, key lime pie is rarely made with actual key limes. Instead, the name now is used to evoke an acid-laced cream inside a biscuit base. I had never tried, let alone made my own KLP, but I have heard good things, and I really like lime. As normal, I made Nigella's version for my starting point.
As much as I enjoyed it, (and I did, as did my fellow eaters) I could tell on my first mouthful that this would be hugely improved with crushed ginger biscuits for the base, instead of digestives. The filling is so light that I feel it needs a robust as possible outside, which the ginger snaps would provide. I tried the pie after the minimum setting time, and 24 hours later- leaving it overnight is a definite improvement to the texture of the filling.

Ingredients
For the base and sides:
250g digestive biscuits (see above)
50g unsalted butter

For the filling:
4 limes
400g (or more likely 397g) condensed milk, preferably chilled
250ml double cream

Method
Grease the sides and base of a a 25cm round springform cake tin, or pie dish. As you can see from the picture, I had neither and used a square cake tin, which worked just fine too. Crush the biscuits finely in a mixing bowl, melt the butter and stir it into the crumbs. It should be a damp, sandy consistency, if it is a little dry add some more melted butter. Press the biscuit mix onto the base of the cake or pie tine, and up the sides as well. Put in the fridge while you get on with the filling.

Zest and juice the limes. Set the zest aside in the fridge, clingfilmed, for decoration later. In a large mixing bowl, mix the condensed milk and lime juice- don't worry if it curdles. Add the cream, and whisk either by hand, electric whisk or freestanding mixture, until it has thickened and increased in volume. It will feel both light and unctuous. By hand, the whisking took about 5 minutes, so it isn't hard work at all. Pour the filling into your prepared base, smoothing out or swirling the top, whatever your aesthetic preference. Let it chill for a minimum of 4 hours, but preferably overnight. Sprinkle with the reserved zest before serving.