Line a slice tray with baking paper.
Break up biscuits into small pieces placing in a large bowl (I like to do this by hand)
Combine butter, syrup and condensed milk in a saucepan, slowly bring to the boil cook a couple of minutes stirring constantly until a thick caramel. (or do this in microwave on high 1 minute, stir, then in further 30 second increments until thickened and caramel)
Add caramel to biscuits and biscuit crumbs, mixing well.
Press into the lined slice tray smoothing the top with the back of a spoon.
Melt chocolate for topping (I do this in the microwave 1 minute on high then in 30 second bursts until melted, stirring well after each time in the microwave)
Add oil to the chocolate and stir well, pour over slice and spread to cover.
Refrigerate until set approximately 2 hours.
Remove slice from fridge 30 minutes before cutting to stop the chocolate cracking.