Preheat the oven to 180°c, gas mark 4, fan 160°c and grease the baking tin, with butter.
For the Shortbread, in a bowl, mix the flour and sugar together, then with your fingertips, so it looks like fine breadcrumbs, rub in the butter. Ensuring the surface is even, press down with your hands into the tin.
Now bake for 20-25 mins, or until the shortbread is a light golden colour. Leave the tin on a wire rack, to cool down for a while.
While your Shortbread is cooking you can place the dark/milk chocolate into one heatproof bowl and melt it over a pan of simmering water. Do the same for the white chocolate too.
Now if your Shortbread base is cooled, pour the caramel over the top so all Shortbread is covered, you shouldn't be able to see any of it.
Now pour the melted dark/milk chocolate over the caramel, similar to before, ensure no caramel can be seen Smooth it out using a pallette knife or spatula. Leave it to chill for 10 mins.
Now drizzle the white chocolate over the top, and then leave to cool (not inside the fridge.)