It's week four in the tent and the baking is getting serious, as the remaining bakers put on their pinnies to pimp up pies and tarts.From the country's oldest known cookbook, we discover the almost 700 year old history of the English custard tart. It might once have been popular at the decadent court of King Richard II but it is now a technical challenge in the Bake Off tent, one which causes more than the intended wobble for the bakers.Starting with what should be a home baker staple, their signature double-crusted fruit pies present a challenge to even the most experienced bakers, let alone the one baker who has a deep-hatred of all things fruit, and the showstopper sorts the bakers from the boys, as they set about making a filo pie centrepiece. Mel and Sue come to their aid as the bakers' nerves are stretched tighter than the filo pastry they are making from scratch.