First, make the shortbread:

1. Preheat the oven to 100C/320F and line a 8 x 8in (20 x 20cm) deep square cake tin with parchment/baking paper. Make sure all the sides are fully covered.
2. Add the butter and sugar to a large bowl and beat with a hand mixer for around 3 minutes – until very fluffy.
3. Sift in the flour and add the salt. Mix with a spoon until just combined. It will look very crumbly and dry and nothing like dough at this stage – fear not!
4. Remove the dough and briefly knead on a clean surface until it sticks together. Press the dough into the cake tin and push it down so it is in an ever layer.
5. Bake the shortbread in the oven for 20-25 minutes until it is lightly golden on top.

Next, make the caramel:

1. Mix together the butter, syrup and condensed milk in a saucepan and place over medium heat. Heat constantly for around 20 minutes until it has turned a deep golden colour. Stir or whisk the mixture constantly while heating to stop it from sticking and burning on the bottom of the pan.
2. Pour the caramel over the shortbread and then transfer to the fridge and allow to set completely. It should be slightly soft to the touch but firm. This should take around an hour. (see note 3)

Finally, add the chocolate:

1. Place a large heatproof bowl over a pan of simmering water. Make sure that the water doesn’t touch the bottom of the bowl. Add 200g of the chocolate to the bowl and stir constantly until just fully melted.
2. Pour the chocolate into a clean bowl and add the remaining 100g grated chocolate. Stir constantly until all the chocolate has melted. (see note 4) Pour over the top of the caramel and then return to the fridge until it’s cooled and set.