Preheat oven to 180C. Grease and line the base and side of three 20cm (base measurement) cake pans.
Prepare the cake mixes using the eggs, milk and butter following packet directions, reserving the icing mixture packets for another use. Divide batter evenly among prepared cake pans. Bake for 1 hour or until a skewer inserted in the centre of each cake comes out clean. Set aside to cool completely.
Meanwhile, to make the Swiss meringue buttercream, combine the sugar and egg whites in a clean, dry heatproof bowl. Place over a saucepan of simmering water and use a balloon whisk to whisk for 3-5 mins or until the sugar completely dissolves and mixture reaches 70°C on a sugar thermometer. Remove from heat and transfer to the bowl of an electric mixer. Whisk constantly for 15 mins or until mixture is thick and glossy and has cooled to room temperature.
With the mixer running, gradually add the butter, 1 piece at a time, whisking well after each addition. Continue whisking for 2 mins or until the mixture is smooth. Reserve one-quarter of the buttercream.
Use a large serrated knife to level the top of each cake. Place 1 cake on a serving plate. Spread with a little of the buttercream.
Continue layering with remaining cake and buttercream. Spread buttercream over top and side of the cake. Tint reserved buttercream pink with red food colouring. Randomly spread a little pink buttercream over the plain buttercream on the side of the cake. Use a large palette knife to smooth the buttercream around side of cake to create a watercolour effect.
Combine the chocolate and cream in a saucepan over low heat. Cook for 2 mins or until the chocolate melts and the mixture is smooth. Set aside to cool slightly.
Use a spoon to drizzle chocolate mixture around the edge of cake. Top with meringues. Set aside to set.