Heat oven to 200C/180C fan/gas 6. Make 3-4 deep slashes length- and widthways in each potato, to make a criss-cross pattern. Sprinkle over a little sea salt and insert a sage leaf into slits of each hedgehog. Put in a roasting tin, add the fat or oil and roast for 45 mins. You can do this up to a day ahead; keep in fridge until ready to cook. Increase oven to 220C/200C fan/gas 7. Roast for 30 mins until crisp and golden.