Bring a few inches of water to a boil in your pot.
Place a heatproof bowl on top of it with the egg whites and sugar.
Whisk until they are extremely hot to the touch.
Pour the whites and sugar into a mixing bowl and whisk until cool and doubled in size, 8 minutes.
Reduce the mixer to medium low and add a few cubes of butter, then increase the speed until incorporated. Continue until all the butter is added,
Add the vanilla then whip for 2 minutes until light and fluffy.
Divide the buttercream into three, then thoroughly mix each puree into each portion of buttercream.
While the cupcakes are cooling fill the piping bags, one for each flavour.
If you have a coupler, attach your piping bags together.
Pipe your icing on your cupcakes.