Soak dried mushrooms in 2-1/2 cups/625 mL warm water until soft, 20 to 30 minutes. Drain, reserving soaking liquid and ensuring mushrooms are clean of grit. (If using trumpet or morel mushrooms, break in half to check inside.) Chop finely. Let soaking liquid stand until sediment settles to bottom.

In soup pot or Dutch oven, melt butter with oil over medium heat; fry onions, stirring often, until light golden, 12 to 15 minutes. Add soaked mushrooms and garlic; fry, stirring, for 2 minutes. Add fresh mushrooms; cook, stirring without breaking slices, until mushrooms are wilted, about 8 minutes. Stir in parsley, vinegar, salt and pepper. Increase heat to medium-high; sauté until mixture is dry. Stir in flour; cook, stirring, for 2 minutes.

Pour in mushroom soaking liquid, leaving sediment behind. Add stock and sherry (if using); stirring, bring to boil. Reduce heat to low; simmer, covered, for 50 minutes. Stir in cream; return to simmer. Remove from heat; stir in parsley and/or chives.

Makes 6 to 8 servings.