Clean, wash and cut the leek into bite-sized pieces. Fry briefly in 1 tablespoon of hot fat. Deglaze with 100 ml water and white wine. Season with salt, pepper and curry. Cook for about 10 minutes.
Add cream, sprinkle with sauce thickener, bring to the boil again briefly and season to taste. Fry sausage in hot oil while turning for about 8 minutes. Then cut into slices and add to the vegetable sauce.
Boil up the milk. Remove the pot from the heat and stir in the puree flakes. Wash apple, quarter it, remove seeds. Cut pulp into small cubes. Peel and chop onion. Fry both in the remaining hot fat for about 4 minutes.
Season with coarse pepper. Pour over the mashed potatoes. Sprinkle everything with fresh herbs and serve garnished with lemon.