Place the biscuits in a food processor and process until finely crushed. Add butter. Process until well combined. Press biscuit mixture over base and side of a 5cm-deep, round 24cm (base measurement) pie or ovenproof dish. Place in the fridge to chill.

Preheat oven to 160°c/140°c fan forced. Cook sweet potato in a saucepan of boiling water for 15 minutes or until tender. Drain, reserving 80ml of cooking liquid. Transfer the sweet potato and reserved liquid to the clean food processor. Process until smooth (you need about 425g puree). Transfer to a large bowl.

Add milk, eggs, sugar, cinnamon, ginger and cloves to puree. Use a balloon whisk to whisk until well combined. Pour over biscuit base. Bake for 1 hour or until filling is just set. Place in fridge overnight to chill.

To make meringue, stir sugar and 60ml water in a saucepan over low heat, brushing down the side of the pan with a wet pastry brush to prevent sugar crystals forming, until sugar dissolves. Increase heat to medium-high. Cook, without stirring, for 3-4 minutes or until the mixture reaches 115c (soft ball stage) on a sugar thermometer. While syrup continues to cook, use electric beaters with whisk attachment to whisk egg whites and cream of tartar in a bowl until soft peaks form. When syrup reaches 120°c (hard ball stage) and with beaters on low speed, gradually add syrup to egg shite mixture. Increase speed to high. Whisk for 10 minutes or until thick, glossy and cool.

Spoon meringue over chilled pie. Use a flat-bladed knife to make peaks. use a cook's blowtorch to caramelise the meringue. Serve.