First either line a 9" baking tin with non stick paper or grease it with non stick cooking spray.
Crush the gingernut biscuits and melt the butter.
Mix the butter with the crushed biscuits and press into the prepared tin in an even layer and set into the fridge.
Caramel Filling;
Place the condensed milk, golden syrup and butter in a saucepan on a medium heat and allow them to melt together.
Turn up the heat to high and while continuously stirring, boil the caramel for at least 5 minutes. The longer you boil the caramel, the darker it will be.
Pour the caramel over the base and place in the fridge for at least 2 hours to set.
Topping;
Once nearly set, melt the white chocolate and spread over the caramel.
Allow the white chocolate to set slightly at room temperature before slicing and then placing in the fridge to fully set.
I would give this at least two more hours but you could check it after one.
Notes
*If you don't gingernuts, any ginger flavoured cookie will do or alternatively you could crush Graham crackers or digestives and add 1 teaspoon of ginger powder to the mixture.