Cashew meringue and buttercream layer cake

Method

1. To make the cashew meringue, preheat the oven to 150ºC. Using a pencil, mark a circle with a 20 cm diameter onto three separate sheets of baking paper, then turn the paper over. Grease three baking trays and line with the baking paper.
2. Place 195 g of the roasted cashews and the cornflour in a food processor and process until finely ground. Roughly chop the remaining cashews. Add half of the chopped cashews to the ground cashew mixture and reserve the remainder to decorate the cake.
3. Using an electric mixer, whisk together the egg whites, lemon juice and salt to soft peaks. Whisking continuously, gradually add the sugar. Whisk for a further 5 minutes, or until the sugar dissolves and the meringue is thick and glossy. Fold in the vanilla and the cashew mixture until just combined. Divide the meringue over the baking paper circles and spread to an even thickness.
4. Bake the meringues for 45 minutes, swapping the trays every 15 minutes, until golden and dry to the touch. Turn off the heat and cool the meringues in the oven with the door left ajar for 30 minutes. Remove from the oven and cool completely.
5. To make the mousse filling, place the sugar and 80 ml water in a small saucepan and stir over medium–high heat until the sugar dissolves. Brush down the side of the pan with a wet pastry brush to remove any sugar crystals, then bring to the boil. Cook for a further 10 minutes, or until the syrup reaches 115ºC on a sugar thermometer (soft-ball stage).
6. Meanwhile, using an electric mixer, whisk the egg yolks for 5 minutes. Reduce the speed to low and whisking continuously, gradually pour the hot syrup down the side of the bowl until combined, then whisk on high speed for 5 minutes, or until thick and cool.
7. Transfer half of the egg yolk mixture to a large clean bowl, reserving the remaining mixture for buttercream. Add the cashew paste and honey, and whisk to combine. Using an electric mixer, whisk the cream to firm peaks, then fold into the mousse.
8. To assemble the cake, remove the meringues from the paper, then place two rounds on a clean work surface. Divide the mousse filling between the two rounds, and spread over evenly, leaving a 1 cm border. Stack them one on top of the other on a serving plate. Top with the remaining meringue, then freeze for 45 minutes, or until firm.
9. To make the buttercream, use an electric mixer to whisk the butter, piece by piece, into the reserved egg yolk mixture until combined and fluffy, then whisk in the rum.
10. Spread a thin layer of buttercream over the top and side of the cake, then spread over the remaining buttercream. Press the reserved chopped cashews around the side of the cake to decorate. Serve immediately or freeze for later; bring to room temperate to serve.