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Start off by weighing all ingredients carefully. Was the potatoes, peel them and slice into quarters. Wash the leek and cut into rings. Chop the onion and garlic and put them into a small bowl.
Put the pan on high fire, add in the sunflower oil. Saute the onion, garlic and orange peel. Pour in the beef broth along with the milk into the pan and stir. Bring to a soft boil, then add in the potato quarters with the leek rings.
Remove the orange peel when the potatoes are boiled and soft enough. You can test of the potatoes are ready by poking them with a fork. If the fork goes in easily, then the potatoes are well cooked.
Mix everything by using an immersion blender. ADD parmesan cheese to liking. Season with some pepper and salt.