Cut the ends off of the potatoes so that they stand on one end. Reserve the ends.
Hollow out as follows... cut a tube through the potato, starting through one of the cut ends, keeping the knife about 3mm away from the edge, and cut right through to the other cut end. (see poorly drawn instructions). Slice through this and push the sections through. Your potato should now be hollow.
Cut a face into the potato, coat in beef dripping and pop in the oven in a roasting pan. Turn occasionally until cooked and slightly crispy on the outside
Chop the potato innards into 1/2inch pieces and boil until very soft.
mash the potato innards and mix with the cheese and onion, or whatever else you chose (bacon, grated cheese, beans, tuna, whatever).
Stuff the potato innards into the potato "pumpkin heads" and serve as a side dish.