Step 1

Preheat the oven to 160C/140Fan/Gas Grease and line an 9x9 (23cm) inch square baking tin with baking paper, making sure the paper rises above the tin by a couple of inches so you can easily lift it out later.

Step 2

To make the shortbread, cream the butter and sugar together with a wooden spoon until light and pale. Add the flour and gently mix it all together until you have a dough. You might need to get your hands in at this stage. Place the dough in the tin and press it out evenly so that it fills the tin. Bake for 20-25 minutes or until very light golden brown around the edges. Leave to cool slightly in the tin.

Step 3

For the caramel, place all the filling ingredients in a saucepan and place over a low to medium heat, stirring constantly until the sugar has dissolved.

Step 4

When the sugar has dissolved competely, turn up the heat to medium high and bring the mixture to the boil, constantly stirring. Watch it very closely and try not to let the mixture catch on the base of the pan - if it does, little brown bits will start to appear. If this happens, turn the heat down to low-medium again and stir like mad. Keep stirring until the caramel has darkened slightly and is thicker. This should take around 8-12 minutes, but it depends on your hob, the pan you're using and the ingredients.

Step 5

If you're making the caramel with a tin of Carnation caramel, place the caramel, butter and caster sugar in a medium sized heavy based pan over a low to medium heat. Allow the indredients to melt together, stirring occasionally until the sugar has completely dissolved. Increase the heat to medium-high and bring to the boil, stirring constantly until the caramel has thickened slightly. If little brown bits start to appear, this means the caramel has caught on the base of the pan - so remove from the heat immediately and stir like crazy.

Step 6

Pour the caramel evenly over the cooled shortbread base and allow to set for at least one hour before adding the chocolate topping.

Step 7

Once the caramel has set, melt the chocolates separately. Pour the milk chocolate all over the caramel, tilting the pan so you get an even covering. Using a teaspoon, drop little spoonfuls of white chocolate over the milk chocolate. Using a knife, swirl the chocolate together to create a pretty pattern. Leave the shortbread to set for a couple of hours. I don't usually put it in the fridge, but you can if your kitchen is very warm. The chocolate will lose some of its shine though.

Step 8

When the chocolate has set, remove the shortbread from the fridge (if you didn't set it at room temperature) and leave for about 15 minutes to take the chill off (if you try and cut it straight from the fridge the chocolate will crack) Using a very sharp knife, cut into squares,