• Spray the baking pan, 9 x 13 x 1 inch, with non-stick cooking spray or brush some oil and then line with a parchment paper on the bottom and the side
  
• Preheat oven to 350 F (180 C) for a conventional oven. Lower the temperature by 20 degrees for a convection oven.
• You will also need a 7-inch round cake pan with removable bottom, with about 3 inches height to assemble the cake later. I line the side with an acetate sheet, which makes it easier and neater. You can skip this step if you don't want to
  

Prepare the sponge cake:

• In a large mixing bowl, whisk egg yolks, oil, and coconut milk until combined.
  
• Sift in the cake flour, and salt.
  
• Whisk to mix until combined and no lumps
  
• Make sure the egg whites are at room temperature. Place egg whites in a mixing bowl of a stand mixer fitted with a whisk attachment. Whisk until foamy on medium speed and then add cream of tartar and whip again for another minute
  
• Add 1/3 of the sugar and continue to add sugar until you use it all up.
• Whip until the egg white develops a medium-soft peak. When you lift the meringue up it will hold up its shape but the tail will bend. Do not whip until stiff peak. The cake will crack when you shape it later
  
• Fold about 1/3 of the meringue into the egg yolk batter
  
• Use a whisk to fold or whisk until mix and continue to fold in the next 1/3 until you use up all the meringue and the batter is smooth.
  
• For the last 1/3, switch back to spatula and make sure you swipe the bottom of the bowl to make sure the batter and the meringue is well-combined. The batter should be smooth and triple in volume
  
• Divide the cake batter into 2, about 200-230 grams each.
  
• Add pandan essence to one and fold to combine
  
• Put the pandan batter into a piping bag and the plain batter into a different piping bag
  
• Pipe the batter diagonally (as shown in the photo), alternating with the plain batter
  
• Gently tap the baking sheet on your working surface several times to pop any air bubbles
  

Bake the cake:

• Bake in a preheated oven for 30 minutes and then switch to convection mode (fan mode) and bake for another 3-4 minutes or until the top is golden brown and dry to touch. If you don't have convection mode, bake another 5 minutes and check to make sure the top is golden brown and dry to touch. It is important that the top is dry to touch
  
• Remove the cake from the oven and then lift it out from the pan immediately to a cooling rack and peel off the parchment paper from 4 sides. This helps to prevent wrinkles on the surface. Let it cool down like this for 5-6 minutes
• After 5-6 minutes. Place a new piece of parchment paper, larger than the cake, on top of the cake and flip over to the other side. Peel off the parchment paper. Let the cake cool down completely before assembling
  

Assembling the cake:

• Trim off the 4 edges to make it neat
  
• Use a 6-inch ring cutter to cut out the cake to cover the base of the pan. If you don't have one, use a 6-inch round cake pan or anything round as a template and use a sharp knife to cut out a 6-inch round
  
• Then cut out strips of cake to cover the side of the pan. You want to make sure the cake strips reach the rim of the pan.
  
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Prepare the white chocolate mousse filling:

• Bloom the gelatin with water and let it sit for 5 minutes to soften. Then you can microwave it in a burst of 10 seconds until the gelatin melts.
  
• Bring the coconut milk just to a gentle simmer. Do not let it come to a boil. Remove from the heat. Add the finely chopped white chocolate pieces and stir until the chocolate melts. Add melted gelatin and whisk again.
  
• Add pandan essence, egg yolk one at a time and keep whisking until mixture is smooth then add another one and whisk. Strain the mixture to make sure there are no lumps
  
• In a mixing bowl, add cold heavy cream and powdered sugar. Whip with a handmixer over medium speed until it thickens slightly but not forming any peak yet.
  
• Add the white chocolate mixture and whip again for 10 seconds or so over medium-low speed. It won't be fully combined yet, but we don't want to overwhip the cream
  
• Switch to a spatula and fold the mixture to make sure they are thoroughly combined
  
• Pour the mixture into the pan and gently smooth the top
  

Chill the cake:

• Chill the cake in the refrigerator for at least 6 hours or overnight for the best result

Finish up assembling:

• Remove the cake from the fridge. Push the cake up and remove the side of the pan and gently peel off the acetate sheet
  
• Garnish with top with some shaved white chocolate