Puy lentil cassoulet with walnut crust

Warming and comforting, this rustic, peasant-style cassoulet is loosely based on the French meaty equivalent, yet it works brilliantly with the earthiness of the Puy lentils and lots of veg. The crust of garlicky walnut crumbs also adds that extra something. Serve in large shallow bowls with crusty bread for dunking and a crisp green salad.