Melt your milk chocolate with the butter in either a microwave at 30-second intervals or in a bowl on top of a saucepan with boiling water in it.
Once melted pour it over the top of your caramel.
Quickly melt the dark chocolate and dollop it in into your milk chocolate in 4 to 6 dollops.
Then quickly melt your white chocolate and do the same, dollop it into your milk chocolate base.
Then using a knife or the handle of a spoon or folk swirl the dark and light chocolate around until it makes a pretty pattern, then leave it to fully cool down and set. At least an hour if you can 2 hours would be better.
Use a sharp knife that has been run under very hot water to slice the tray into 12 squares.
Then serve and enjoy. These squares will keep in an airtight tin for up to 5 days.