Pour the boiling water over the dried mushrooms in a bowl and set aside to soak.

Preheat a heavy stockpot over medium heat for about 1 minute, then spray it twice with the vegetable oil. Add the leeks and sauté for about 3 minutes, stirring constantly, until translucent. Add the flour and curry powder. Stir with a wooden spoon until the leeks are well coated. Add the milk and bouillon cube. Raise the heat to high and cook just until bubbles begin to form around the edge.

Reduce the heat to low and whisk until all ingredients are thoroughly combined. Stir in the fresh mushrooms and cook for 5 minutes.

Meanwhile, remove the reconstituted mushrooms from their soaking liquid, strain, squeeze out excess moisture, and roughly chop. (Save the soaking liquid for another soup or sauce; here it would thin the soup too much and curdle the skim milk.) Add to the stockpot and cook for 1 minute more. Stir in the sherry.

Garnish with the chopped chervil.