Lynnette asked for a rainbow cake for her birthday. I split three cakes to make the six layers. The outside is Italian Buttercream topped with sugar crystals for extra sparkle. It could have used a little more icing between the layers, but for a first attempt I was really happy with how it turned out.
The secret to a good rainbow cake is to be generous with the food colouring. Start with a good quality paste colour (I like Wilton’s.) The cake will get a little darker than the batter but not that much.