Soak dried mushrooms in warm water until softened, 20 to 30 minutes.
Drain mushrooms, reserving soaking liquid. Rinse mushrooms and squeeze dry. Chop coarsely, discarding any tough stems. Strain soaking liquid through coffee fileter and reserve.
Melt butter in heavy large saucepan over medium heat. Add shallots and cook until soft, stirring occasionally, about 3 minutes. Add dried and fresh mushrooms, salt and nutmeg. Cook until almost most of liquid evaporates, stirring occasionally, 6 to 8 minutes. Add flour and stir 3 minutes. Whisk in stock and 2-1/2 cups mushrooms soakig liquid. Bring to boil, whisking constantly. Reduce heat and boil gently until soup thickens slightly, skimming surface occasionally, 40 minutes.
Whisk 1/2 cup cream into soup. Simmer 5 minutes; degrease if necessary. If desired, thin soup with any remaining mushroom soaking liquid and more cream. Season with salt and pepper. Sprinkle with chives and serve.