Add cocoa powder to the base mix if you want a darker, more bitter, dark chocolate taste to the biscuit base. Alternatively use Oreo® cookies instead of digestives for the same effect.
This is a very easy recipe but the instruction to `pour` the chocolate mixture over the coffee layer is wildly optimistic! Mine ended up more like a ganache consistency and getting it to take the form of an even layer involved a series of incentives that surprised my children and the result was more marbled than I would have preferred. However, the cream top layer did a good job of hiding its imperfections and I'm sure the taste was unaffected. - 21 Sep 2014