Peel and finely chop the onion. Clean and wash the leek. Cut the white of the leek into thin rings. Wash, quarter and core the apples. Finely dice quarters, sprinkle with lemon juice and put aside covered.
Cut the rest of the apples into small pieces.
Heat 1-2 tablespoons of fat in a saucepan. Brown the onion, leek rings and apples in it. Sprinkle with curry and sauté briefly. Deglaze with 3/4 l water, bring to the boil and stir in broth. Simmer covered over medium heat for 15-20 minutes.
Finely chop the leek green. Heat 1 tablespoon of fat in a frying pan. Sauté the leek and apple cubes briefly. Puree the soup with a hand blender and pour through a sieve as desired. Set aside 4 tsp. crème fraîche, stir in the rest.
Season everything with salt, pepper and sugar.
Arrange the soup and spread the apple-porree-mix on top. Garnish with the remaining crème fraîche and a little curry.