Method

• 1.
  Preheat oven to 180°C/160°C fan-forced. Grease base and side of 3 x 18cm round springform pans and line with baking paper. Ensure paper extends 2cm above sides of pans. Place butter and 400ml water in a large saucepan and stir over medium heat until butter has melted. Remove from heat, add white chocolate and stir until completely melted and combined. Set aside to cool.
• 2.
  Combine both flours, sugar and a generous pinch of fine salt in a stand mixer fitted with the paddle attachment. Mix on low speed until combined, then pour in the chocolate mixture. Continue to beat while you add the eggs and vanilla paste. Beat until well combined and smooth. Divide the mixture among prepared pans, then smooth top with an offset spatula. Bake for 1 hour, or until golden brown and a skewer inserted in the centre of each cake comes out clean. Cool cakes completely in pans on a wire rack. Carefully remove cakes from pans and wrap in plastic wrap. Chill overnight.
• 3.
  For the white chocolate ganache, place the chocolate in a large heatproof bowl and set aside. Bring the cream to the boil in a small saucepan over medium heat and pour the hot cream over the chocolate. Use electric handheld beaters to beat until well combined. Add butter and continue beating until mixture is smooth. Pour ganache into a clean, deep tray and cover surface directly with plastic wrap until ready to use. (If making the ganache at the same time as the cakes, store overnight at room temperature.)
• 4.
  Just before assembling, transfer 1½ cups of the white chocolate ganache to a bowl. Stir through the 2 tbs 100s and 1000s until well combined. When ready to assemble, trim the domed tops of the cakes using a serrated knife and a ruler, so the trimmed cakes all measure 4.5cm high. Place a cake on a serving plate, using a little of the ganache to secure it in place.
• 5.
  Spread half the ganache with sprinkles onto the top of the cake and then place the second cake on top. Press second cake down gently to make sure cake is level. Spread top with remaining ganache with sprinkles and place final cake on top. Press down gently to make sure the top is level and flat. Use an offset spatula to smooth out any ganache that has come out from between the layers of the cake.
• 6.
  Apply remaining white chocolate ganache to the top and outside of the cake, spreading evenly. Place the assembled cake on a wire rack over a deep baking tray (to help catch the sprinkles). Pour the 500g 100s and 1000s into a bowl and, using your hands, press sprinkles all over the cake, covering it evenly and completely.
• 7.
  Serve cake decorated with some of the macarons, with remaining alongside.