Preheat your oven to 180C/160C Fan, and line a 9x9inch deep square tin with parchment paper.
Cream together the caster sugar and unsalted butter until smooth.
Mix in the plain flour until a dough is formed. It will be crumbly but the ingredients will be evenly dispersed!
Firmly press the mixture into the bottom of tin and bake in the oven for 20-25 minutes until pale golden on top!
Once baked, remove from the oven and leave to the side.
In a large saucepan pour the condensed milk, unsalted butter, caster sugar and golden syrup and melt on a medium heat till the sugar has dissolved – stir frequently to stop anything from catching.
Once the caster sugar has dissolved, turn the heat up high and let the mixture come to boiling point and boil for 5-7 minutes stiring constantly so that the mixture doesn't catch.
BE CAREFUL as the mixture is VERY hot and can burn you if it splashes back! The mixture will be ready when it has changed to a slightly darker golden colour, and has thickened to a soft fudge texture!
Crush your 2-3 pinches of sea salt into the salted caramel and mix in - pour the salted caramel onto the shortbread base and leave to completely set.
Once chilled, melt the milk and dark chocolate and pour over the caramel.
Swirl them together with the end of a skewer so it forms a pretty pattern.
Chill the shortbread back in the fridge for another 1-2 hours until the chocolate has gone hard.
Chop your shortbread into the separate pieces and enjoy!
This will keep in an airtight container for at least 1 week, or you can freeze for up to 3 months – if they last that long!
If your caramel is rock solid when you remove it from the fridge, you have slightly over done it. Not to worry though, when you pour the chocolate on, leave it to set at room temperature rather than in the fridge and it should soften the caramel slightly.
If you struggle to cut your shortbread and tray bakes without the chocolate cracking on top, set it at room temperature rather than in the fridge and it'll be softer so therefore won't crack when you cut it!
Alternatively you can warm up a large sharp knife with boiling water and try cutting your slices using this!
I use Maldon Sea Salt as it tastes delicious and I like my caramel salty so I use the 3 pinches - I really really recommend using Sea Salt over ground fine salt as the taste is better and it's easier to use compared to the fine salt where you could easily add in far too much.