Wash the fruit and vegetables. Cut the peppers into large pieces, and peel and dice the potatoes. Also peel the apple and cut it into cubes.
Cut the leek into rings and braise in a saucepan with oil. Add the pepper, potato and apple pieces and briefly sauté. Pour in the hot vegetable stock, add the finely chopped chilli pepper, and simmer for about 20 minutes. In parallel, beat the cream until stiff.
When the vegetables are cooked, puree the soup and season with salt, pepper and curry powder. Stir in the plain yoghurt. Pour the soup into a bowl, add the cream as a topping, garnish with the cress and serve.