1 tablespoon extra-virgin olive oil, 
4 cups sliced shiitake mushroom 
4 cups sliced baby bella mushrooms
1 cup diced onion or shallot
½ cup diced celery
3 cloves garlic, minced
½ teaspoon dried thyme
½ teaspoon salt
½ cup dry sherry
4 cups "no-chicken" broth or mushroom broth
1 cup water
1½ cups chopped walnuts - Available at Slivers
2 teaspoons sherry vinegar
½ teaspoon ground pepper

Mushroom-Walnut Topping
1 tablespoon extra-virgin olive oil
1 cup coarsely chopped shiitake mushroom 
1 cup coarsely chopped baby bella mushrooms
½ cup chopped walnuts
Pinch of salt
2 tablespoons sliced fresh chives

Preparation

Heat 1 tablespoon oil in a large pot over medium-high heat. 
Add 4 cups shiitake mushrooms, 4 cups baby bella mushrooms, onion (or shallot), celery, garlic, thyme and ½ teaspoon salt and cook, stirring occasionally, until tender, 7 to 10 minutes. 
Add sherry; increase heat to high and simmer, stirring often, until the sherry has evaporated, 2 to 3 minutes. 
Add broth and bring to a simmer. 
Puree water and 1½ cups walnuts in a blender until completely smooth, about 1 minute. 
Pour into the soup; return to a simmer. 
Reduce heat to medium-low and cook, stirring often, until the vegetables are very soft, about 5 minutes longer.

Meanwhile, prepare topping: 
Heat oil in a medium skillet over medium heat. 
Add mushrooms and cook, stirring often, until soft, about 2 minutes. 
Add walnuts and salt. 
Cook, stirring occasionally, until hot, about 1 minute more. 
Puree the soup with an immersion blender or in a regular blender (in batches, if necessary) until very smooth. (Use caution when blending hot liquids.) 
Stir in vinegar and pepper. Serve the soup topped with the mushroom-walnut mixture and chives.