Add the light brown sugar, golden syrup, dairy free butter and soy cream to a saucepan and place over a medium heat. Mix well until everything is combined, the butter is melted and the sugar is dissolved.
Continue to simmer on low to medium heat for another 15 to 20 minutes (stirring continuously so it doesn't burn) to form a runny caramel sauce. The sauce will thicken slightly when it cools, so don't let it thicken too much on the heat. Stir in the salt and let sit for 15 minutes.
After 15 minutes pour the caramel sauce into the biscuit base and transfer to the fridge to set for 2 hours.