Whizz together the 2 cups of thickened cream, ½ cup custard, and ¼ cup icing sugar until thick.
Place a layer of Biscoff biscuits on the bottom.
Spread ½ of the cream mixture onto the Biscoff biscuits.
Pour caramelised sweetened condensed milk over the top. To caramelise the condensed milk, place an unopened tin into a saucepan, cover with water and boil for 2 ½ - 3 hours (prefer 2 ½ hours).
Place another layer of plain biscuits (like Arrowrott, Morning Coffee or Scotch Finger) on top.
Spread the remaining cream mixture over the layer of biscuits.
Melt together 75ml thickened cream and 120g chocolate, then pour over the final cream layer.
Crush biscuits and sprinkle over the top of the chocolate ganache layer.
Cover and refrigerate for at least 4 hours, but overnight is better.
