Rainbow Cake with Buttercream

Ya. It's rainbow cake again. This time I did it for my niece's fullmoon. Feeling stress as I wanna make the best I could for her. Did some trial and error. Some ended with nice colour but not nice cake. After few rounds of discussion, my darling shifu mentioned that if heavy cream then heavy cake. I've decided to follow her success rainbow cake. I added 2 eggs to make it 6 eggs cake. I was so happy that my cake turn out to be a nice looking cake. It's tall and soft. Hopefully they will like it. Each colour batter is bout 380g. End result of each layer bout 2.5cm tall. Weighed the cake. Total bout 2kg. Wow big cake! So here you go. Following recipe is for 2 layers only. So please do own calculation.

Original recipe: http://dequeenkitchen.blogspot.com/2012/04/rainbow-layered-butter-cake-with-swiss.html

Ingredients:
220g plain flour
180g sugar
170g unsalted butter
2 3/4 teaspoon baking powder
1 teaspoon vanilla essence
180ml milk
2 eggs

1. Cream soften butter & sugar till light and fluffy.
2. Add one egg at a time.
3. Add milk and vanilla essence.
4. Add flour.
5. Separate batter into 2 equal portion
6. Add different coloring to each portion
7. Pour into different baking tins.
8. Shake the baking tins a little to even out the batter.
9. Bake at 180°C for about 20 minutes or till cooked.
10. Leave on wire rack to cool.

Buttercream:
(A)
350gm soften butter
150gm cream margarine

(B)
180gm icing sugar

1. Cream (A) till well blended.
2. Add in (B) and beat till light and fluffy.
3. Add desired colouring.