Melt the butter over a low heat. Place the biscuits in a food processor and blitz to a fine crumb. Slowly mix in the melted butter and then spread the mixture evenly in the bottom of a flan or cake tin. Press down to create a firm base and then chill in the fridge while you prepare the rest of the recipe.
In a bowl, whisk together the cream and condensed milk until stiff. Zest and juice the limes and then mix through the cream. Pour this mixture on to the chilled biscuit base and refrigerate for at least 2 hours.
Once the pie has set, whisk the egg whites until they start to go fluffy. Add the sugar and whisk until you have stiff peaks. Spoon the meringue on top of the pie and use a blowtorch to lightly brown the meringue.
«You can enrich this pie by adding the discarded egg yolks to the cream mix and then baking the pie at 180'C for 15 minutes before chilling in the fridge.»