Step 1

Preheat oven to 140C/120C fan forced. Draw five 18cm circles on 3 sheets of baking paper. Place, ink-side down, on 3 large baking trays.

Step 2

Place 335g (2 1/4 cups) cashews and 80g (1/2 cup) icing sugar in a food processor. Pulse, scraping down side of the bowl with a spatula, until the mixture resembles coarse crumbs (see tip). Transfer to a bowl. Sift the remaining icing sugar into the bowl. Stir until combined.

Step 3

Use electric beaters to whisk the egg whites in a clean, dry bowl until soft peaks form. Add caster sugar, 1 tbs at a time, whisking constantly until the mixture is thick and glossy. In 3 batches, fold the cashew mixture into the egg white mixture until just combined. Spoon mixture into a piping bag fitted with a 1cm plain nozzle.

Step 4

Pipe the meringue mixture from the centre of 1 circle on prepared tray in a coil motion until circle is covered. Repeat to make 5 meringue discs in total (see tip for what to do with any leftover mixture). Bake, rotating trays halfway through cooking, for 45-55 minutes or until meringue is dry and crisp. Set aside on trays for 10 minutes to cool slightly before carefully transferring discs to a wire rack to cool completely.

Step 5

Meanwhile, make the rum buttercream. Stir the caster sugar and 125ml (1/2 cup) water in a saucepan over low heat, brushing down side of pan with a wet pastry brush to prevent sugar crystals forming, until sugar dissolves. Increase heat to medium and bring to the boil. Cook, without stirring, for 8 minutes or until mixture reaches 115C (soft ball stage). While the syrup cooks, use electric beaters to whisk egg yolks in a bowl for 8-10 minutes or until pale and creamy. Remove syrup from heat and set aside for 1 minute or until bubbles subside. With beaters on low speed, gradually add sugar syrup to egg yolk mixture. Increase speed to high and whisk for 10 minutes or until thick, glossy and almost at room temperature. Gradually add the butter, beating well after each addition, until mixture is smooth and creamy. Add the rum and beat until well combined. Spoon mixture into a large piping bag fitted with a 1cm fluted nozzle.

Step 6

Coarsely chop the remaining cashews. Pipe a small amount of buttercream onto a serving plate. Place a disc on top to secure. Pipe peaks of buttercream around edge of disc. Pipe buttercream into centre and spread to cover. Sprinkle with one-fifth of the chopped cashews. Continue layering with discs, buttercream and cashews 3 more times. Top with remaining disc. Pipe peaks of remaining buttercream over top of cake. Sprinkle with remaining cashews. Place in fridge for 2 hours or until set. To serve, set aside for at least 30 minutes or until buttercream is room temperature