From Ned Bell on Cook Like A Chef (potato episode).
Peel sweet potatoes and slice them evenly on a mandoline, putting them in water as you finish the slices in order to keep their colour. Take the white and light green part of leeks, halve them lengthways, slice them across into thin semicircles, and wash them.
Grease a shallow oval casserole dish and layer the vegetables in it - first a layer of sweet potato slices, making sure to overlap them, then season with salt and pepper, then sprinkle over some leeks, then crumble over a little bit of some nice, sharp blue cheese.
Repeat these layers, maybe four times, ending with a layer of sweet potato slices.
Grate over some nutmeg, drizzle over some melted ghee or butter, and pour a bit of whole milk in around the edges of the dish.
Bake in a 190C/375F/Gas Mark 5 oven for about 40 minutes until nicely browned on the top.
Cut along the long axis of the oval terrine, then cut into wedges. Run a knife around the outside of the dish to free the edges, then take wedges out using a pie slice.
You can sprinkle over more blue cheese to serve, and garnish with slices of leek. On the programme they served it with some sliced pork tenderloin.