Preheat oven to 180 degrees F 82.2 degrees C and line a square slice or cake tin with greaseproof paper (Tray dimensions 24cm x 5cm, 9 inch x 2 inches)
Add shortbread biscuits to the bowl of the food processor and blitz for 15-20 seconds till they are a fine crumb. Transfer to mixing bowl
Add butter to heatproof glass jug. Microwave butter for 1 min till melted
Pour melted butter over biscuit crumb and stir to combine. Transfer to lined slice tray and push to flatten using a glass
Place slice tray into the middle shelf of the oven and bake for 15 mins, till light golden brown. Use oven mits to remove from oven when done and set on cooling rack
Add sweetened condensed milk, brown sugar and butter to large microwave safe jug. Microwave for 3 mins, then stir to combine. Microwave for a further 3 mins. Then remove jug from microwave, place on heatproof surface and whisk consistently for 2 mins.
Pour caramel over cooked biscuit base. Place in the oven and cook for 10 mins
Use an oven mit to remove from the oven and allow to cool on wire rack
Add chocolate melts and olive oil to heatproof jug, microwave in 30 seconds lots x 4, stir till all of the chocolate is melted. Pour melted chocolate over caramel base and then transfer to the fridge to set
Allow slice to set for an least 2 hours (or overnight), then remove from the fridge and use a sharp knife to cut into pieces. Store in the fridge for up to 1 week.