Peel the potatoes and cut into large even-sized pieces. Place in a pan of cold salted water and bring to the boil. Simmer for 10 minutes, then drain and return to the pan for a minute or so to dry out.
Preheat a large roasting tin with 1 ½cm of dripping (goose or duck fat) for a few minutes until just smoking. Place the flour in a small bowl, season generously and add soft thyme leaves, if using. Place the potatoes in a colander and toss them in a handful of the seasoned flour. You’ll need to do this quite vigorously so the edges start to break up slightly.
Arrange the potatoes, flat-side down in the hot fat and baste the tops, adding the garlic cloves at this point for a different dimension. Place in preheated oven and cook for 20 minutes at 200 degrees Celsius before turning the potatoes over. Cook for a further 20 minutes, then pour off the majority of the fat. Cook for a final 20 minutes until crispy around the edges and golden brown. Sprinkle with some sea salt and serve.