This is my fall back dessert. My Mum brought the recipe back from Canada when she and Dad lived there before I was born. I don't make this very often as it is quite rich, but, oh so yummy. I also usually make 2 as it freezes so well without the topping. And then I put a seasonal fruit topping of my choice when it has defrosted.
Sometimes I use digestive biscuits for the base, and sometimes chocolate chip or even ginger biscuits. You can ring the changes, it's all good.