Prepare the vegetables: Peel the onion, carrot, and potatoes and cut them into pieces. Cut the leek lengthwise, rinse thoroughly between the layers if necessary, and slice into rings or half-rings. There’s no need to cut the vegetables particularly small or neatly since the soup will be blended later.
Sauté the onion and leek: Heat the olive oil in a large pot and sauté the onion until translucent. Add the leek and cook for another 1–2 minutes.
Cook the soup: Add the carrot, potatoes, water, vegetable bouillon powder, and cashews and bring to a boil. Cover and simmer for about 15 minutes, until the potatoes and carrot are tender.
Blend the soup: Blend the soup only until smooth and creamy. Season to taste with salt, black pepper, and freshly grated nutmeg.
Beluga Lentil Topping (if using)
Cook the Beluga lentils: If you’re making the Beluga lentil topping, start with the lentils so they can cook while you prepare the soup. Simmer them in plenty of water for about 30 minutes, until tender but still slightly firm. Drain once done.
Season the Beluga lentils: Finely chop the garlic and briefly sauté it in a little olive oil. Add the chili powder and Beluga lentils and cook for about 2 minutes. Deglaze with the balsamic vinegar and stir in the chopped parsley.
Serve: Divide the potato leek soup among bowls and spoon the Beluga lentils on top. Sprinkle some more chopped fresh parsley on top of the lentils.