Key Lime Pie

Ingredients

• 200g digestive biscuits or graham crackers
• 2 tbsp caster sugar
• 100g unsalted butter, melted
• Pinch of salt
• 4 large egg yolks
• 1 tin sweetened condensed milk, 397g
• 150ml key lime juice, from about 25 key limes or 12 regular limes
• 2 tbsp finely grated lime zest
• 300ml double cream, well chilled
• 2 tbsp icing sugar
• 1/2 tsp vanilla extract
• Extra lime zest, to finish

Before you cook

• Heat the oven to 175C
• Zest the limes before juicing them, then squeeze the juice and strain out the pips
• Crush the biscuits to fine crumbs in a food processor or a bag with a rolling pin
• Separate the eggs and let the yolks come to room temperature

Steps

1. Mix the biscuit crumbs, caster sugar, salt and melted butter until the crumbs look like damp sand.
2. Press the mixture firmly into a 23cm pie dish, pushing it up the sides with the base of a glass to get an even wall.
3. Bake the crust for 10 minutes until it smells toasted, then leave it to cool on a rack for 15 minutes.
4. Whisk the egg yolks with the lime zest for 2 minutes until they thicken and pale slightly.
5. Pour in the condensed milk and whisk for another 2 minutes.
6. Add the lime juice in a slow stream while whisking, and watch the mixture visibly thicken as the acid works on the milk.
7. Pour the filling into the cooled crust and smooth the top.
8. Bake the pie for 15 minutes, until the centre still has a slight wobble but the surface no longer looks wet.
9. Cool the pie completely at room temperature for 1 hour.
10. Chill the pie in the fridge for at least 3 hours, or overnight for the cleanest slices.
11. Whip the cold cream with the icing sugar and vanilla to soft peaks that just hold their shape.
12. Spread or pipe the cream over the chilled pie, finish with a shower of lime zest, and cut with a hot dry knife.