Cover the veal with boiling water and poach gently. Add the onion and the seasonings tied up in a cheesecloth to make a bouquet garni. Skim the stock while the veal is poaching to keep the liquid clear. When the cubes are tender, after about 1 hour, remove the bouquet garni and the veal. Make a roux with the butter and flour and add to the veal stock. Bring to a light boil and seaon with salt, white pepper and lemon juice. Add the veal, sautted mushrooms and white asparagus together with a small amount of liquid from the asparagus can. Heat well and serve on rice.