For the Chocolate Mousse, half fill a medium saucepan with water and bring to a simmer over a medium heat. Place chocolate and butter in a medium bowl, sit over the saucepan of simmering water and stir until melted. Remove the bowl from the heat and set aside.
Place cream into the bowl of a stand mixer fitted with a whisk attachment. Whisk to stiff peaks then set aside.
Place egg and egg yolk into the bowl of a stand mixer fitted with a whisk attachment and whisk until slightly thickened and foamy. Meanwhile, place sugar and 75g water into a small saucepan over medium heat and heat to 121C. When sugar syrup reaches temperature, remove from heat and gradually add to the eggs, whisking on high speed until the mixture has thickened and cooled, about 5 minutes. Remove egg sugar mixture from mixer and use a spatula to fold in the reserved melted chocolate and butter mixture until fully incorporated. Fold through the whipped cream, cover and set aside in fridge.
For the Roasted Macadamias, line a baking tray with baking paper. Spread macadamias onto the lined baking tray and roast until golden, about 3-4 minutes. Remove from oven and sprinkle with lemon myrtle and pinch of salt. Set aside.
For the Meringue Cake, place egg whites into the bowl of a stand mixer fitted with a whisk attachment and whisk until lightly foamy.
While whisking on high speed, gradually add the sugar and continue to whisk until sugar has dissolved and meringue is thick and glossy. Take 1 cup of the meringue mixture and place into a medium mixing bowl with remaining ingredients for the Meringue Cake and whisk until smooth. Set remaining meringue mixture aside for the Lemon Myrtle Meringue.
Using a palette knife, spread batter onto a lined tray to a thickness of 1mm and bake until golden brown, about 10 -15 minutes. Remove from oven and set side to cool.
Decrease oven to 120C.
For the Lemon Myrtle Meringue, line a baking tray with baking paper. Using a palette knife, spread reserved meringue over the lined baking tray to a thickness of 1mm. Dust lightly with the ground lemon myrtle and bake until crisp but not browned, about 10-12 minutes. Remove from oven and allow to cool then break into shards and set aside.
For the Sour Grapes, place vinegar, sugar and ½ cup water into a small saucepan and bring to the boil. Add grapes, remove from the heat and allow to stand for 30 minutes. Drain and set aside.
For the Kaiserfleisch Crumb, place kaiserfleisch into a large frypan and place over a medium heat. Cook until crisp and dark golden in colour. Remove from pan and set aside on kitchen paper. Transfer to food processor and pulse to a fine crumb. Set aside.
To serve, arrange fresh and Sour Grapes around serving plates. Scatter with Roasted Macadamias and pieces of fresh goats cheese between grapes. Sprinkle with Kaiserfleisch Crumb and top each plate with 2 quenelles of Chocolate Mousse. Add shards of Lemon Myrtle Meringue and Meringue Cake. Finish with finely grated dark chocolate.