1. Wash the asparagus. Cut 2 inches (5 cm.) off the tips and save them for another use. Do not peel the stalks but cut them into 15-inch (3-cm.) pieces. 2. Bring the stock or broth to a boil in a soup pot. When it bubbles, add the asparagus pieces and sugar. Turn down the heat, cover, and simmer for 20 minutes. 3. Blend and pass through a fine strainer (a chinois if possible), pressing on the solids with a spoon to extract as much liquid as possible. Put the soup back in the pot, bring back to a boil, and boil about 30 minutes more. 4. Thoroughly mix the cornstarch in a bowl with 1 tablespoon cold water. Beat the yolk and cream together in a bowl large enough to hold all the soup. 5. When the soup in the pot has been reduced by about half, whisk in the cornstarch mixture. Boil for 1 minute, whisking constantly, and then gently pour everything into the bowl with the egg-cream mixture, whisking as you pour. 6. Pour the contents of the bowl back into the soup pot and heat very gently in order to thicken. Stir with a spatula and turn off the heat at the first sign of boiling. Blend. Season with salt as necessary.