Peel and halve the onion. Wash the meat. Bring 1 litre of salt water, onion, bay leaf and peppercorns to the boil. Add the meat and let it simmer at low heat for about 30 minutes.
Wash the asparagus and cut off the woody ends. Cook the asparagus in boiling salted water for about 10 minutes, drain and collect the asparagus stock. Remove meat from the stock, let it cool down a bit and cut into cubes.
Clean, wash and quarter the mushrooms. Heat the fat in a pot. Brown the sausage and mushrooms in it. Dust with flour, sweat and deglaze with 1/4 l asparagus stock and milk. Bring to the boil and simmer at medium heat for about 5 minutes.
Cut the asparagus into pieces and heat in the ragout. Wash the herbs, dab dry, chop finely and stir into the ragout. Season with salt and pepper and season with lemon juice.