Key Lime Pie

Preheat the oven to 160°C/140°C fan/325°F/Gas 3 and place a 20cm fluted flan tin on a baking sheet.

Combine the digestives, pretzels, sugar and melted butter in a large bowl until you have a mix that holds together when pressed between your fingers (add a little more melted butter if it's too dry and sandy).

Tip the mixture into the flan tin and press in an even layer across the bottom and up the sides until you have a firm pie crust. Bake for 10 minutes, or until lightly golden and firm to touch. Remove from the oven and allow to cool completely.

To make the filling, remove the zest from the limes in strips using a zester and set aside for the candied lime zest. Juice the limes into a measuring jug until you have 120ml juice.

Whisk the egg yolks in a bowl using a hand-held electric whisk until they are thickened and lighter in colour. Whisk in the cream of tartar and condensed milk on low speed, a little at a time, until combined. Continue to whisk as you pour in the lime juice until incorporated. Pour into the cooled crust.

Bake the pie for about 15 minutes, or until the filling has just set around the edges but the centre still has a slight wobble. Remove and allow to cool slightly before transferring to a wire rack to cool completely.

While the pie cools, prepare the topping. Whip the cream and icing sugar together in a large bowl until stiff peaks form. Using a spatula, fold through the yoghurt and rum (if using). Place dollops of the cream on top of the cooled pie and create swirls. Chill in the fridge for about 2 hours - if you can wait!

Make the candied lime zest. Put the golden caster sugar and water into a small pan. Place over a medium heat and bring to the boil, then turn down to a simmer. Add the strips of lime peel and cook gently for 25 minutes until the peel has softened and the syrup has thickened.

Dust a sheet of baking parchment with golden caster sugar. Lift the softened lime peel out of the pan with a slotted spoon and roll in the sugar to coat. Leave to cool until hardened. (This will keep in an airtight container for up to a month.)

When you are ready to serve, remove the pie from the fridge and decorate with the candied lime zest. Enjoy!