Heat half of the goose fat. Gently roast potato slices in it. Adjust the heat so that the potatoes become soft and lightly brown. Add a little goose fat if needed.
Turn the potatoes occasionally, making sure the slices stay whole. Just before the end, add the garlic to the frying pan; it should not brown too much or it will become slightly bitter.
Season with salt and pepper and sprinkle with parsley just before serving.