Wash and peel the potatoes then cut into your preferred size (but make sure they’re as similar in size as possible). Sink the potatoes into cold, salted water and bring to a boil then reduce the heat so the water is bubbling and cook the potatoes for 5-7 minutes.
Drain the potatoes in a colander and leave to stand for a few minutes. Give the potatoes a good shake until the outer edges are fluffy. This will act like a sponge for your oil and give them extra crispiness. Pour your potatoes onto a tray that’s large enough for them not to be piled on top of one another then leave to air-dry for an hour.
Place the goose fat and vegetable oil into a roasting tray and heat in the oven at 180ºc for 4-5 minutes.
With great care, add the potatoes to the hot fat and gently coat, add the sea salt, garlic, sprigs of thyme and orange zest.
Roast through the oven until crisp – the trick is to turn them only once or twice while basting with the goose fat.