How to Make It
Heat 1 teaspoon of the oil in a heavy nonreactive medium saucepan. Add the shallots and cook over moderate heat, stirring, until slightly softened but not browned, about 4 minutes. Add the Marsala and cook just until evaporated, about 2 minutes.
Add the white mushrooms, shiitake stems, thyme, 1/2 teaspoon salt and 1/4 teaspoon pepper and cook over moderately high heat for 10 minutes, stirring occasionally. Add the chicken stock and bring to a boil. Reduce the heat to low, cover and simmer for 30 minutes. Strain the soup and return it to the saucepan; you should have about 3 cups.
Heat the remaining 1 teaspoon oil in a large nonstick skillet. Add the shiitake mushrooms and season with salt and pepper. Cook over moderate heat, stirring occasionally, until softened and lightly browned, about 5 minutes.
Ladle the hot soup into shallow soup bowls and add the shiitakes. Garnish with the parsley and serve.