Method

• 1.
  For the cake, preheat the oven to 160°C fan-forced. Grease three 18 cm round cake tins, at least 3 cm deep, and line the bases and sides with baking paper. In a large bowl or the bowl of a stand mixer, gently fold together the dry ingredients until combined. Put the dark chocolate and coconut oil in a clean, dry, heatproof bowl over a saucepan of just-simmering water (the water should not touch the base of the bowl). Gently stir with a silicone spatula until melted, then set aside to cool to room temperature. Using a hand-held mixer or stand mixer fitted with the paddle attachment, slowly add the chocolate mixture to the dry ingredients and beat on low speed until just combined. Beat in the eggs, one at a time, followed by the milk and vanilla extract. Mix until combined, being careful not to over-mix. Divide the batter evenly between the prepared cake tins and bake for 45 minutes, or until a wooden skewer inserted into the centre comes out clean. Remove from the oven and allow to cool in the tins for at least 1 hour, before turning out onto a baking rack to cool completely. As a tip, melting chocolate in the microwave can be a great time saver. Place the chocolate and coconut oil in a clean, dry, microwave-safe bowl and microwave at 50% power, stirring at 30-second intervals with a silicone spatula until melted.
• 2.
  For the buttercream, place the sugar and egg whites in a heatproof glass bowl. Set the bowl over a saucepan of just-simmering water (the water should not touch the base of the bowl), and whisk until the sugar has dissolved and the egg whites are slightly warm to the touch (at least 40°C). (You can omit this step entirely if you are using pasteurised egg whites, and instead, simply place the sugar and egg whites directly into the mixer.) Transfer the mixture into the bowl of a stand mixer. Using the whisk attachment, whisk on high speed until the mixture has formed stiff and glossy peaks, around 10–15 minutes. Meanwhile, put the dark chocolate in a clean, dry, heatproof bowl over a saucepan of just-simmering water (the water should not touch the base of the bowl). Gently stir with a silicone spatula until melted. Remove from the heat and allow to cool slightly. Switch to the paddle attachment on your stand mixer. Add the butter to the egg whites, in thirds, and beat on high speed after each addition until incorporated. Don’t be alarmed if the buttercream appears curdled – it will become light and fluffy once whisked for around 2–5 minutes (I absolutely promise!). Beat in the melted chocolate and add the vanilla. Continue to beat until fluffy, and then beat on low speed to eliminate air bubbles. Cover the bowl with plastic wrap and set aside at room temperature in a cool environment until needed. As a tip, melting chocolate in the microwave can be a great time saver. Place the chocolate in a clean, dry, microwave-safe bowl and microwave at 50% power, stirring at 30-second intervals with a silicone spatula, until melted.
• 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 medium saucepan over medium heat and bring to the boil without stirring. As soon as it boils, remove the saucepan from the heat. Stir the sweetened condensed milk and pre-soaked gelatine through the sugar syrup. 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 three bowls and tint with the gel colours to 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, you will need a small food-safe paint brush. Working on a cake turntable, secure the bottom layer of cake onto a cake board with a small dollop of chocolate 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. Repeat the process with the second and third layers, leaving the final top layer uncovered. 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; this will make it much easier to apply 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 the cake in the freezer to chill for at least 1 hour. Remove the frozen 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 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 different areas of the cake (see opposite). Once the cake is fully covered, use a hair dryer to give the surface a quick blast to create a marbled effect. Let the glaze continue to drip and set for about 3 minutes. Use large spatulas to carefully place the finished frozen cake onto a cake board. Decorate the bottom edge of the cake with edible metallic rock candy. Use a clean food-safe paint brush to lightly splatter edible silver paint over the cake to create a galaxy of stars (you can practise on a piece of paper or paper towel first) and then finish with a sprinkling of edible stars. Place the cake into the refrigerator. Allow it to thaw there for at least 1 hour, then leave it 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.
  For storage, this cake is best enjoyed at room temperature. It can be stored in an airtight container in the refrigerator for up to 5 days. You can bake the cake 2 days in advance and store it tightly covered with plastic wrap at room temperature, or freeze it for up to 2 months. Thaw it overnight in the refrigerator before decorating. The buttercream can be made ahead, as can the glaze, which can be refrigerated for up to 7 days. When needed, gently reheat it in the microwave until the correct pouring temperature is reached (35°C). Pour the colours into separate bowls or jugs and use immediately.