Peel the potatoes and cut them into chunks roughly the same size.
Rinse the potatoes under cold water and put them into a large pot.
Cover with cold water and bring to a boil.
Boil the potatoes for 5 minutes.
Preheat your oven to 200C.
Pour the goose fat into a large roasting pan and put into the oven.
Drain the potatoes into a colander.
Now put 5-7 potato chunks into a sieve and swig them around vigorously to roughen up the surfaces. Repeat with all potatoes.
Once the goose fat is hot, put the potatoes into it and spoon some of the fat over the potatoes.
Roast for 30 minutes.
Tear off the leaves of the rosemary and bash the garlic cloves.
Add to the potatoes, mix everything to cover with the fat and return to the oven.
Roast for another 45 minutes until golden.
Serve whilst hot.
Tip: Peel and chop them the day before and keep them in cold water over night.