Start by pre-heating your oven to 180c/350f. Also grease and line a 9x12 inch cake tin.

Crush the biscuits until you get fine crumbs. You can either do this in a food processor or just put them in a food bag and hit them with a rolling pin.

Mix the crushed biscuits with the melted butter, then add this into your prepared cake tin. Press it down until you get an even layer. Leave this aside

In a pot, add the butter and dark chocolate. Place this pot over medium-low heat, and heat until you get a melted smooth mixture. You could also do this in your microwave. Leave this aside to cool down.

In a large bowl, add the eggs and both sugars. Whip this until the mixture lightens in colour and almost doubles in volume. It's easiest to do this with an electric mixer but it can be done by hand, just whisk aggressively.

Pour the cooled butter/chocolate mixture into this and whisk.

Now add the flour, cocoa powder and salt. Whisk just until you get a smooth batter.

Pour this into the tin, on top of the shortbread layer. Bake for around 35-40 minutes, or until a toothpick inserted into the centre comes out with a few moist crumbs on it. Once baked, leave aside to cool down.

In a pot, add the butter, condensed milk, golden syrup and sugar. Place this over medium-low heat.

You want to keep heating this mixture, whiles constantly stirring, until the mixture turns into a golden, caramel colour. Make sure not to increase the heat to speed up the process, the caramel will burn.

Take this off the heat and mix the salt into it.

Pour this on top of your baked brownie and spread it out, then put this in your fridge.

In a bowl, add the chocolate and oil. Heat this in your microwave at 30 second intervals, until all the chocolate has melted and you get a smooth mixture.

Pour this on top of the caramel layer and spread it out.

Now leave this in the fridge for a minimum of 2 hours so that all the layers can set up, I like to just leave it in the fridge overnight.

Once chilled, take it out of the tin, cut into it and enjoy!