Easy Key Lime Pie

Ingredients
For the base:
3½ oz (95 g) butter
6 oz (175 g) digestive biscuits
2 oz (50 g) Grape-Nuts breakfast cereal / Wheat-a-bix or Oat-a-bix
For the filling:
1 level tablespoon grated lime zest (zest 3 limes)
5 fl oz (150 ml) lime juice (juice 4-5 large limes)
3 large egg yolks
14 oz (400 g) condensed milk
To finish:
a little crème fraîche
lime slices
Pre-heat the oven to gas mark 4, 350°F (180°C).

Method

Traditional Key lime pie has always had a crumb crust, and I have discovered recently that the addition of Grape-Nuts gives the whole thing extra crunch. So begin by placing the butter in a pan over the lowest heat to melt, then crush the digestive biscuits. The easiest way to do this is to lay them out flat in a polythene bag and crush them with a rolling pin, rolling over using a lot of pressure. Now empty the contents of the bag into a bowl and mix in the Grape-Nuts, then add the melted butter and mix well. Next place the butter-crumb mixture in the flan tin and, using your hands, press it down evenly and firmly all over the base and up the sides of the tin. Then place it on the baking sheet and bake on the centre shelf of the oven for 10-12 minutes, or until crisp and golden brown.
While that's happening, place the egg yolks and lime zest in a bowl and, using an electric hand mixer, whisk them for about 2 minutes, or until the egg has thickened, then add the condensed milk and whisk for another 4 minutes. Finally, add the lime juice and give it another quick whisk, then pour the whole lot on to the baked crust and return it to the oven for another 20 minutes, or until it feels just set when you lightly press the centre with your little finger. Now remove it from the oven and, when it's completely cold, cover it with clingfilm and chill until needed. Serve cut in slices with crème fraîche and a twist of lime for decoration