Peel the potatoes and onion and cut both into identical thin slices.
Put the sunflower oil into a heavy frying pan and heat until hot but not smoking. Fry the speck lardons until fat begins to run, then add the potato and onion slices and the bratwurst. Sauté for 10–15 minutes, until the potatoes are nicely browned.
Add the garlic and marjoram, and season with salt and pepper. T