• Line the base and sides of a loose-based deep-fill 23cm/9” tin with grease-proof paper.
• Preheat the oven to 160c or equivalent.

Make the Base

• Whizz 400g Dark Chocolate Digestive Biscuits with 4 tbsp Cocoa Powder in a food processor or blender until it is of a vaguely sandy consistency.  
  
• If using a stand mixer, you may wish to use your fingers to break up any larger chunks remaining.
  
• Melt 100g Salted Butter in a small bowl (microwave) or pan (hob).
• Add the melted butter to the broken biscuits and and whizz again.
  
• Tip the base mixture into the lined tin and press into the base and as far up the sides as you can manage. Try to make the base as even as possible.
  
• Place in the fridge to chill whilst making the filling.

Make the Filling

• Separate 5 Large Eggs and put the egg yolks into a mixing bowl (I used the stand mixer again but it isn't necessary). Put the whites aside for the time being.
  
• Add 2 x 397g Tin of Condensed Milk to the egg yolks and whisk until well combined.
• Zest enough limes to get 3 tbsp Zest and and juice enough limes to get 240ml Lime Juice. Add to the egg yolks. Don't let this sit without mixing as the lime will start to 'cook' the egg yolk.
  
• Stir for a minute to combine. You only need to mix this together, not whip it. 
  
• Put the crust-lined tin onto a baking sheet and pour in the filling.
  
• Place the pie in the oven and bake for 10–15 minutes, until the filling is just set but has not changed in colour.
  
• Leave to cool thoroughly in the fridge (at least several hours).
• The pie can then be removed from the tin. Peel off the greaseproof paper carefully before decorating.
  

Make the Meringue Topping

• Combine 220g Caster Sugar and 80ml Cold Water in a small pan.
  
• Stir over a low heat until the sugar dissolves. Then increase the heat to bring it to the boil.
  
• Reduce the heat to medium and brush down the sides of pan with a clean, wet pastry brush to remove any sugar crystals.
• Boil until the syrup reaches 121°C. This will take about 10-15 minutes. This is where you will ideally require your sugar thermometer.
  
• Meanwhile, start whisking the 5 reserved egg whites with 0.25 tsp Cream of Tartar, ideally in a stand mixer. Whisk until soft peaks form.
  
• Once the sugar syrup reaches temperature and with the motor of the mixer continuing to run, gradually pour the hot sugar syrup into the whisked egg whites.
  
• Continue to whisk at medium speed until the meringue has cooled to room temperature and is thick and glossy. This will take roughly another 10-15 minutes so be patient!
  
• Fill a disposable piping bag with the meringue mix and your choice of nozzle.
• Pipe the meringue onto the top of the chilled pie.  
  
• You can use whatever design you like. I went with a star nozzle and worked my way in from the outside then adding more layers on top of that but working inwards to create a point. I have previously used a round nozzle.
  
• Using a blowtorch, carefully and slowly caramelise the outside of the meringue to a light golden brown.
  
• Serve!