2) Shortly before serving, frost the cake with the whipped cream. Spread the whipped cream on generously and create cloud-like swirls by lightly dragging a palette knife through the whipped cream and gently pulling up to make peaks.
3) Decorate the platter around the cake with strawberry coulis and sprinkle the whole thing with confetti sprinkles. As the cake is sliced, a rainbow of frosting will be revealed on the inside.
For the vanilla buttercream:
1) In a double boiler over hot water melt the butter. Remove from the heat and allow to cool for 5 minutes.
2) In an electric stand mixer add the butter and icing sugar and beat until the mixture resembles chalky beads. Add the vanilla and the milk, 1 tbsp at a time, until the buttercream is a spreadable consistency. Beat again until fluffy, adding more milk if necessary.
3) Place the buttercream into 5 bowls and colour one red, one orange, one yellow, one blue and one green.
For the strawberry coulis:
1) Combine the strawberries, water, sugar and lemon juice in a saucepan and cook over medium heat until the sugar is dissolved and the strawberries are quite soft.
2) Puree the mixture in a blender, strain through a fine strainer and cool. Place in a squeeze bottle.