It is the Bake Off semi-final, and it is Patisserie Week, with just four bakers remaining. In the signature challenge, the bakers are once again butter-bashing and folding their pastry to achieve perfect lamination for a difficult French pastry.In the technical challenge, Paul has set the bar high. He is testing the bakers' patisserie prowess with a yeast-based cake that has a fruity top and delicate chocolate work.The showstopper is the bakers' last chance to prove they have what it takes to make it to the final, with a multiple mini-cake bake. The timings are crucial to achieve the high-end finish the judges are looking for.Which of the bakers will impress Mary and Paul enough to earn their place in next week's final, and who will be leaving the tent?