Beat butter until light and fluffy - about 5 minutes.
Add vanilla and sea salt, beat for 1 minute.
Add powdered sugar and beat to combine.
Weigh your mix and separate equally into three bowls.
Melt the white chocolate. Once fully melted, pour into a bowl to cool.
Melt your milk chocolate in the same bowl, no need to wash it. Pour into another bowl to cool.
Once the white chocolate is cool, add it to one of the bowls with the buttercream. Repeat steps with the milk chocolate and the dark chocolate.
To the bowl with the dark chocolate, add the sugar and cocoa.
Onto a piece of plastic wrap, spread each buttercream in lines next to each other.
Roll the plastic wrap and press to seal. Place in piping bag and decorate as you like.