Радужный торт

RECIPE For the cake - 9 tbsp whole milk 1 ½ tsp vanilla extract Various colour pastes (red, orange, yellow, green, blue & purple) 750g soft unsalted butter 750g caster sugar 9 large free-range eggs 750g sifted self-raising flour Butter & flour for preparing the cake tins For the buttercream - 400g soft unsalted butter 900g sifted icing sugar 5-6 tbs whole milk ½ tsp vanilla extract