Wash the potatoes well under running water and pat dry.
Locate the flattest side of your potato and stick a skewer through it at about 0.5 cm. from the bottom and then cut wafer-thin notches in the thickest side of the potato with a sharp knife up to the skewer.
Carefully remove the skewers and place the potatoes on a plate in the microwave. Precook the potatoes for about 3 minutes on the highest setting. You will see that the potatoes steams well afterwards.
Meanwhile preheat the BBQ to 210°C.
Place a cast iron skillet on the fire in which the potatoes fit. Add the goose fat, crush the garlic and add the rosemary to the skillet. Fry briefly while putting pancetta slices into some of the notches.
Place the Hasselback potatoes in the skillet and cover with the melted fat. Let the potatoes cook (+-1h) until you notice that the slices fall open and start looking crispy. Pour the melted fat from the skillet over the potatoes with a spoon every 10 minutes.
Let the Hasselback potatoes cook another 10 minutes after the point where you think they are crispy. Prick with a skewer to test if the inside is cooked well.
Serve with a nice piece of grilled meat or fish. Have a nice meal and smoke on!