Clean the leek and cut into thin slices. Peel and chop the carrots and potatoes. Peel, fillet, peel and chop 1 1/2 oranges. Squeeze 1/2 orange.
Briefly sauté the leek and carrots in the oil. Now fill up with the broth. Add the potatoes and cook for about 15 minutes. Next add the orange and lemon juice and the chopped oranges. Rinse with salt and pepper. Stir in 100 g crème fraîche and then puree the soup with a hand blender until frothy. Arrange on plates or in soup bowls and top with a teaspoon of crème fraîche.