Peel and wash the potatoes and cut into small cubes. Clean and wash spring onions and cut the white part into small pieces. Peel the onion. Heat the fat in a saucepan and fry the onion, the white of the spring onion and the diced potatoes.
Deglaze with vegetable stock, bring to the boil and simmer for about 10 minutes. Meanwhile cook the salmon tortelli in boiling salted water for about 4 minutes. Wash dill, tarragon and chervil, dab dry and pluck.
Cut leek green into small rings. Add leek green, 2/3 of the herbs and cream to the boiling soup and puree finely with the cutting stick of the hand mixer. Season to taste with salt, cayenne pepper and lemon juice.
Bring the soup to the boil again. Spread the salmon tortelli on 4 plates, pour the hot soup over them and garnish with the remaining herbs.