Method

• 1.
  For the cake, preheat the oven to 160°C fan-forced. Grease two 18 cm round cake tins, at least 3 cm (1 ¼ inches) deep, and line the bases with baking paper. Using a hand-held mixer or a stand mixer fitted with the paddle attachment, beat the butter, black sesame paste and sugar on medium for 3 minutes, or until light, pale grey and creamy. Add 2 tablespoons of the flour, then gradually add the vanilla and eggs, one at a time, beating after each addition until well combined. Gently fold in the remaining flour and the hot water all at once. Divide the mixture equally between the cake tins. Bake for 20–25 minutes, or until the centre of each cake springs back when lightly pressed. Remove from the oven and allow to cool for 5 minutes, before turning out onto a baking rack to cool completely. Cover and set aside until needed.
• 2.
  For the buttercream, using a hand-held mixer or a stand mixer fitted with the paddle attachment, beat the butter and black sesame paste on high speed for 10–15 minutes, or until doubled in volume and very pale grey in colour. Add the icing sugar, one-third at a time, and beat until well combined and fluffy. Add the vanilla and beat until combined and fluffy.
• 3.
  For the glaze, place the white chocolate in a medium heatproof bowl and set aside. Combine the sugar, glucose and 110 ml water in a saucepan over medium heat and bring to simmering point without stirring. Remove from the heat and stir in the condensed milk and pre-soaked gelatine. Pour the hot ingredients over the white chocolate and emulsify with a stick blender (or you can mix thoroughly with a spatula/spoon), being careful not to create air bubbles. Divide the glaze between two bowls and tint each one with gel colours of your choice to achieve the desired shades. Place plastic wrap on the surface of each glaze colour and allow to cool to around 35°C. Once at the right temperature, use immediately. Don’t fret if your glaze cools before you are able to use it. Simply gently re-heat the bowls in the microwave in 5–10 second bursts, stirring in between.
• 4.
  To assemble, working on a cake turntable, secure the bottom layer of cake onto a cake board with a small dollop of buttercream and then gently twist in place. Use an offset spatula to spread a 5 mm layer of buttercream right to the edge of the cake, then press the second layer of cake on top. Use an offset spatula to gently crumb-coat the cake with a thin layer of buttercream. Chill the cake in the refrigerator for 10–20 minutes, or until firm; this will make it much easier to pipe and smooth the buttercream onto the outside. Apply another layer of buttercream to the chilled cake and use a cake scraper to smooth the side. Finally, use an offset spatula to smooth the top of the cake by gently pulling inwards from the outer edge of the cake into the centre, cleaning the excess buttercream off the spatula with each scrape. Place in the freezer to chill for at least 1 hour. Remove the cake from the freezer and gently lift it from the cake board (you can use a hot knife and a large spatula for this). Place the cake on a cooling rack or on a sturdy object slightly smaller than your cake (such as an upside-down cake tin) on top of a large baking tray (to catch the run-off glaze). Working quickly, alternate pouring each coloured glaze onto the centre of the cake, then work your way out to the edges. Once the cake is fully covered, use a hair dryer to give the surface a quick blast (this creates a marbled effect). Let the glaze continue to drip and set for about 3 minutes. Use large spatulas to carefully place the frozen cake onto a cake board. Adorn it with chocolate spheres or other round chocolates and then place into the refrigerator. Allow to thaw in the refrigerator for at least 1 hour, then leave at room temperature for at least 1 hour before serving (so your friends won’t be eating firm chunks of buttercream and hard cake).
• 5.
  To store, this kind of cake is best enjoyed at room temperature, but it will last refrigerated in an airtight container for up to 5 days. The cake can be baked in advance and stored, wrapped in plastic wrap or in an airtight container, for up to 2 days in the refrigerator. The Swiss meringue buttercream can be made ahead of time. Baked cakes covered with buttercream can be covered in two layers of plastic wrap and frozen for up to 1 month. The glaze can be made ahead of time. Keep the individual colours stored separately in airtight containers in the refrigerator for up to 7 days, and when needed, gently reheat in the microwave until the correct pouring temperature is reached (35°C). Use immediately.