Onions peel and roughly chop. Cut the woody ends off the asparagus. Cut 4 stems diagonally into slices, halve the asparagus head lengthwise. Cut the remaining asparagus into pieces. Peel and chop the potatoes. Wash the chervil, shake dry and put 4 stems aside for garnishing. Chop the remaining chervil coarsely
Melt butter in a pot. Sauté the onions and potatoes in it for about 1 minute, then deglaze with stock, milk and cream. Season soup with salt, pepper and a little saffron and simmer covered for about 10 minutes. Add the asparagus pieces and simmer again for about 8 minutes until the asparagus is soft
Peel the shrimps, except for the tail fin, and remove the intestines. Wash the shrimps and dab them dry. Heat the oil in a pan. Fry the prawns, asparagus slices and heads for 3-4 minutes while turning and season with salt and pepper
Puree the soup and season again with salt, pepper and possibly some lemon juice. Arrange the soup, asparagus and prawns in bowls and garnish with the remaining chervil