Peel and cut up the potatoes into big chunks.
Place in a saucepan and cover with water and a pinch of salt. Bring to the boil and allow to simmer.
When they are about half way cooked removed from the pan and run under cold water to help them cool and stop cooking. In the pan roll the potatoes to fluff them up. Be gentle so they don't break.
Drain them and leave them to cool and dry out. You don't want them to be watery or the fat will spit.
Preheat the oven to 180ºC fan. 30 minutes before you are ready to serve them put a baking tray on the hob with the goose fat and 2 tablespoons of rapeseed oil.
Let it heat up and gently add the potatoes. Don't let it get too hot. Using a spoon, move the potatoes about so they get covered.
Place in the oven and turn every 10 minutes to make sure all the edges get covered and can brown off.
When they are golden brown remove from the oven and put in a serving dish. Stir in a few sprigs of fresh thyme and serve.