Cake

1. Preheat your convection oven to 160°C (320°F).
2. Grease and line three 6 in / 15.24cm round cake tins with vegetable oil and baking paper, then grease again and dust with a tiny amount of rice flour to coat the cake tin.
3. In a large mixing bowl sieve flours, starch, sugar, baking powder, baking soda, salt, and xanthan gum together. Briefly whisk to combine.
4. In a large bowl, mix all remaining wet ingredients together, including zest.
5. Pour liquid into the bowl of dry ingredients and gently mix together until just combined. It will be a very thick mixture. 
6. Pour batter into each cake tin, making sure they have the same amount of batter. Tap the pans gently on the bench to release any air bubbles.
7. Place tins into the middle of your oven and bake for 38 to 41 minutes, or until a skewer poked into the middle comes out almost clean with still a few crumbs.
8. Allow to sit in the cake tins for 20 minutes before running a knife around the outside and turning onto a cake rack. Let it completely cool before assembling your cake. Whilst your cake is cooling, prepare your American Buttercream, see recipe here and make a double batch. Then move onto preparing your lemon curd. See assembling instructions for further details. 

Lemon Curd

1. Melt butter in a small saucepan over medium heat.
2. Remove from the stove and mix in cornflour to form a thick, smooth paste.
3. Return to medium heat and add remaining ingredients. Continue to stir until sugar has dissolved and curd thickens; about 3 minutes.
4. Take off the heat and let it rest for 30 minutes before using.

Assembling The Cake

1. Using a sharp knife, cut the domed tops off all cakes to create perfectly flat rounds. Make sure each cake is exactly the same height. 
2. Place the bottom layer onto your cake board or stand. Using a piping bag with a round nozzle, pipe buttercream around the edge of the cake to create a thick 1 inch border. Fill the centre with lemon curd, reaching only ¾ of the way to the top of the buttercream. Place your 2nd layer on top and repeat the process until you add the final layer of cake on top. 
3. Crumb coat your cake in buttercream, then divide your remaining cream into three bowls. Add a few drops of yellow to the first bowl, add a few more drops of yellow to the second bowl to make it a darker yellow and leave the remaining bowl white. 
4. Fill 3 piping bags with each buttercream. Divide your cake into 3 equal sections and pipe the darkest colour on the bottom section, the 2nd colour on the middle section and the remaining white. 
5. Smooth out the sides with an offset spatula or cake scraper. 
6. Make your drip icing, see recipe here and using a teaspoon, drip small amounts down the side of your cake to create a drip effect. 
7. Add any remaining buttercream from your bowls to one piping bag and add a wide star tip nozzle, pipe the remaining buttercream on top of your cake, around the edge of the cake however you desire. Add lemon slices to the top of your buttercream swirls to finish your decoration and serve!