This puff-pastry topped pie combines the earthy, woodsy flavours of mushrooms (porcini and button) and Puy lentils in a creamy, umami-packed sauce flavoured with fresh tarragon, porcini powder and Dijon mustard. All you need on the side is a nice, sharp salad – but we would never say no to a pile of buttered mash or warm baguette to chase the last of that sauce.