Thinly slice the cremini mushrooms. Dice the onion and mince the garlic and set aside. In a small bowl, pour 1 cup boiling water over the dried mushrooms. Let steep for about 30 minutes. Drain and reserve the liquid. Roughly chop the wild mushrooms and set aside.
In a large Dutch oven or pot, heat 1 tablespoon each of olive oil and butter over medium high heat. Add 1/3 of the sliced cremini mushrooms and sprinkle with a little kosher salt. Sauté until the mushrooms are tender and beginning to brown. Remove from the pot and set aside to use as a garnish later.
Lower the heat to medium. Add the remaining olive oil and butter to the pot along with the diced onion. Cook the onions for about 3-5 minutes until they are softened and beginning to brown. Add the remaining cremini mushrooms and season with a generous pinch of kosher salt. Sauté until the mushrooms begin to brown and any liquid that has accumulated cooks off.
When the mushrooms are browned, add the minced garlic and chopped thyme. Sauté for another minute until fragrant. Add the sherry to deglaze the pan. Allow the sherry to simmer and reduce by half. Stir in the flour.
Add the broth to the pot in 2 or 3 batches, stirring to prevent lumps. Lastly, add the reconstituted wild mushrooms along with the reserved soaking liquid. Add 1 tsp kosher salt and the pepper and then bring the soup up to a simmer. Simmer over medium low heat for about 10 to 15 minutes until the vegetables are tender and the soup has thickened slightly.
Carefully transfer the hot soup to a high-speed blender. Blend on high until smooth. You may need to do this in two batches, depending on the size of your blender. Return the soup to the pot. Stir in the heavy cream and Worcestershire sauce.
Check the consistency of the soup, adding a bit more broth if it is too thick. Reheat the soup until hot. Serve the soup topped with the reserved sautéed mushrooms and chopped parsley. Enjoy!