Preheat the oven to the hottest possible temperature.
Peel the potatoes, and cut each into 3 by cutting off each end at a slant so that you are left with a wedge or triangle in the middle.
Place the potatoes into salted cold water in a saucepan, and bring them to a boil. Boil the potatoes for 4 minutes. Drain the excess water from the potatoes using a colander and then tip the potatoes back into the empty saucepan.
Sprinkle the semolina over the top of the potatoes. Hold a lid firmly on top of the pan and shake the potatoes around to coat them well and so that their edges disintegrate or fuzz and blur a little: this facilitates the crunch effect later.
Place the goose fat into a large roasting tin and heat in the oven until very hot. Then carefully place the semolina-coated potatoes into the hot fat and roast the potatoes in the oven for 45 minutes to an hour or until they are darkly golden and crisp, turning them over halfway through cooking. If the oven is hot enough they probably will not need more than about 25 minutes a side; and it's better to let them sit in the oven (you can always pour off most of the fat and leave them in the tin) until the very last minute.