Preparation Time: 2 1/2 hours

Total Time: 3 hours

INGREDIENTS

White Chocolate Cake

• 90 g good quality white chocolate
• 170 g butter, cubed and at room temperature
• 300 g white sugar
• 3 large eggs, separated
• 2 tablespoons vanilla extract
• 210 g plain/all-purpose flour, + 25 g cornflour (this is an Australian substitute for cake flour. If you have access to cake flour, swap this combination for 310 g cake flour)
• 1 tablespoon baking powder
• 1 teaspoon baking soda
• Pinch of salt
• 180 mL buttermilk

Swiss Meringue Buttercream

• 6 large, fresh egg whites (180 g)
• 300 g white sugar
• 410 g unsalted butter, cut into small cubes and cool, but not cold (leave out of fridge for 15-20 minutes before use)
• 2 teaspoons vanilla extract
• Pinch of salt
• 1/4 cup fresh blackberry puree (about 100 g/half cup fresh berries. If using frozen blackberries, allow to thaw on paper towel and absorb excess liquid before pureeing)
• 150 g good quality white chocolate

METHOD

White Chocolate Cake

1. Preheat the oven to 160°C/320°F fan forced. Grease and line three 7 inch/18 cm round cake tins, or two if you don’t have three!
2. Melt the white chocolate in a medium heatproof bowl over a pot of simmering water. Remove from heat and allow to cool to room temperature, for 10 minutes.
3. In a medium mixing bowl, beat the butter and half of the sugar on medium speed until pale and creamy. Add vanilla and chocolate, and beat just to combine.
4. Add egg yolks one by one, beating well between each addition.
5. In a separate mixing bowl, sift together the flours, baking soda, baking powder and salt. With the beater on low-medium speed, add the dry ingredients alternately with the buttermilk, spoonful and dash at a time, beating between each addition. Beat for another 30 seconds to combine.
6. In a third mixing bowl, whisk the egg whites and remaining sugar until soft, glossy peaks form. Gently fold the egg whites into the cake batter with a large metal spoon.
7. Pour the batter evenly into the 3 tins. If you are using 2 tins, pour 2/3 of the batter into one tin, and the remaining 1/3 into the second tin.
8. Bake the cakes on the centre rack for 20-25 minutes, until a metal skewer comes out clean but moist, and the tops are lightly coloured. If you are baking 2/3 of the batter in one tin, bake this tin for 25-30 minutes, but remember to remove the smaller cake first!
9. Leave the cakes in their tins for 10 minutes, then turn out onto a wire cooling rack, and leave to cool for 20 minutes. The cakes will be very soft and sponge-like. Once cooled, refrigerate the cakes until you are ready to frost. This will firm them up and make frosting much easier.

Swiss Meringue Buttercream

1. In a large heatproof bowl over a pot of simmering water, gently hand-whisk the egg whites and sugar until sugar has just dissolved and mixture appears white (5-10 minutes). Alternatively, use a candy thermometer to whisk until temperature of mixture reaches 70°C/160°F. Ensure you whisk gently but constantly, so that egg whites do not cook.
2. Transfer mixture to the large bowl of an electric mixer, and whisk on medium/low speed until meringue is very thick and glossy and holds its peaks, and the bowl feels neutral to touch. It is very important that you whisk until the bowl no longer feels warm, otherwise the butter will melt when added. Whisk for 10-15 minutes, and if the bowl is still warm, turn mixer off and allow meringue to cool further. This will ensure you do not over-whisk meringue. Double check the temperature of the meringue by turning off the mixer, and dipping a clean finger into the centre of the meringue. It should feel room temperature.
3. Once cooled, swap whisk attachment for paddle attachment. With the mixer on its lowest possible speed, gradually add butter one cube at a time, beating for a few seconds between each addition. The buttercream will suddenly loosen and may appear thin or scrambled as you go, but just keep beating on low speed until all of the butter is incorporated.
4. Meanwhile, melt the white chocolate in a medium heatproof bowl either in the microwave or over a pot of simmering water. Set aside until just cool enough to dip your finger into, this should take about 10 minutes.
5. Once all of the butter is added to the buttercream, continue beating on a low speed for a minute or two. The buttercream should be thick and glossy. If it is too thin, the butter was too soft when added, so refrigerate buttercream for 15 minutes to firm up and then continue beating. If it appears too thick or scrambled (literally like scrambled eggs!) the butter was too cold when added, so keep beating on low speed until buttercream is smooth. Add the salt and beat to combine.
6. Divide the buttercream into 2 bowls. Add the blackberry puree to one bowl, teaspoon at a time, beating vigorously with a spatula or on low speed with an electric beater between each addition. Go slowly, as too much liquid will cause the buttercream to separate…err on the side of caution! If you like, remove half a cup of buttercream from the bowl, and add another teaspoon of blackberry puree to create a darker shade of buttercream. Using a small offset spatula or butterknife, frost the 3 cake layers together using the blackberry buttercream, starting with the darker shade then moving up to the lighter shade.
7. Add the cooled melted white chocolate to the second bowl of buttercream, and beat to combine. Using a little of the white buttercream, frost a crumb coat over the entire cake. This is a very thin coat, and you should be able to see the cake through the buttercream. It forms a seal around the cake so you don’t get crumbs in your pretty frosting! Refrigerate the cake for 30 minutes, until buttercream is firm to touch.
8. Frost the outside of the cake by starting from the bottom with the blackberry buttercream, working 2/3 of the way up the sides of the cake. Frost the top surface with the white chocolate buttercream, then spread it down the top 1/3  of the sides and blur the line between the two colours of buttercream.
9. Refrigerate cake for 30 minutes until buttercream is firm to touch, then use a clean metal spatula, butterknife or benchscraper to smooth the surfaces of the cake. Make sure the cake has been out of the fridge for 45 minutes before serving.

Store the cake covered and refrigerated for up to 5 days, but best served within 1-2 days of baking.

Note: Swiss meringue buttercream can be refrigerated in an airtight container for up to one week, or frozen for up to 6-8 weeks. Simply omit the blackberry puree before refrigerating or freezing the buttercream. Before using it to frost your cake, allow it to cool to room temperature, then beat on medium speed using an electric mixture until it retains its silky, soft consistency. This can take up to 20 minutes, so be patient if the texture looks a little strange. Once smooth, beat in the blackberry puree and away you go! For ease, if possible prepare the SMB immediately before you frost your cake.