It is the quarter final and there are just five bakers left. In the last seven weeks they have been tested on normal cakes, breads, pastries, pies and puddings so the judges are upping the ante. This week's challenges test them on how they cope working with unconventional flours and unusual desserts which push their creativity to the max. For the signature challenge, the bakers must make a loaf using non-traditional wheat flours, encouraged instead to use the rarer flours such as spelt, rye, potato or tapioca flours. Whilst the bakers get busy with their loaves, the programme explores the history of the National Loaf. This culinary creation was borne out of necessity during World War Two, when the Ministry of Food developed a flour to make imports go further and keep the nation healthy in times of rationing. The technical round sees the bakers challenged to each make a dacquoise, made with three layers of fragile coiled meringue, sandwiched with coffee custard and topped with hazelnut praline, a dessert which also happens to be gluten free. For their final challenge, the bakers must push themselves out of their comfort zone to create showstopping novelty vegetable cakes - which must also be dairy free.