Step 1: Prepare the Mushrooms

1. Clean the Mushrooms: Gently clean all the mushrooms. For cremini and oyster mushrooms, you can usually just brush off any dirt with a mushroom brush or a dry paper towel. Shiitake mushrooms might need a slightly damp paper towel. Avoid soaking mushrooms in water as they can absorb it and become waterlogged.
2. Slice or Chop: Slice the cremini mushrooms into ½-inch thick slices. For shiitake mushrooms, remove the tough stems and slice the caps. Oyster mushrooms can be roughly torn or sliced into bite-sized pieces. If using larger mushrooms like king oyster, slice them into rounds or chunks.
3. Set Aside: Keep the prepared mushrooms aside, ready to be sautéed.

Step 2: Sauté the Aromatics

1. Heat Olive Oil: In a large, heavy-bottomed pot or Dutch oven, heat olive oil over medium heat. Make sure the pot is large enough to accommodate all the ingredients comfortably.
2. Sauté Onion: Add the diced onion to the hot oil and sauté for 5-7 minutes, stirring occasionally, until softened and translucent. Do not brown the onions at this stage, just soften them to release their sweetness.
3. Add Carrots and Celery: Add the diced carrots and celery to the pot with the onions. Sauté for another 5-7 minutes, stirring occasionally, until the vegetables start to soften slightly. This layering of sautéing vegetables builds a deeper flavor base.
4. Add Garlic: Add the minced garlic to the pot and sauté for 1-2 minutes more, until fragrant. Be careful not to burn the garlic, as it can become bitter.

Step 3: Sauté the Mushrooms

1. Increase Heat: Increase the heat to medium-high. This will help the mushrooms brown nicely and develop flavor.
2. Add Mushrooms: Add all the sliced and chopped mushrooms to the pot. It might seem like a lot of mushrooms, but they will cook down significantly.
3. Sauté Mushrooms: Sauté the mushrooms, stirring occasionally, for 8-10 minutes, until they release their moisture and then begin to brown and caramelize. Initially, the mushrooms will absorb the oil and then release their liquid. Continue cooking until this liquid evaporates and the mushrooms start to brown and become tender. Browning the mushrooms is crucial for developing a rich, savory flavor in the stew.

Step 4: Deglaze and Build Flavor

1. Add Red Wine (Optional): If using red wine, pour it into the pot and scrape up any browned bits from the bottom of the pot using a wooden spoon or spatula. This process, called deglazing, adds a layer of flavor and prevents sticking. Cook for 2-3 minutes, allowing the wine to reduce slightly and the alcohol to evaporate.
2. Add Flour (or Gluten-Free Alternative): Sprinkle the flour (or gluten-free alternative) over the vegetables and mushrooms. Stir well to coat everything evenly. Cook for 1-2 minutes, stirring constantly, to cook out the raw flour taste. This step helps to thicken the stew slightly.
3. Pour in Broth: Gradually pour in the vegetable (or chicken) broth, stirring continuously to prevent any lumps from forming.
4. Add Flavor Enhancers: Stir in the soy sauce, balsamic vinegar, and Worcestershire sauce (if using). Add the bay leaves and thyme sprigs.
5. Season: Season with salt and black pepper. Start with 1 teaspoon of salt and ½ teaspoon of black pepper, and adjust to taste later. Add a pinch of red pepper flakes if you like a little heat.

Step 5: Simmer the Stew

1. Bring to a Simmer: Bring the stew to a gentle simmer over medium heat. Once it’s simmering, reduce the heat to low, cover the pot, and let it simmer gently.
2. Simmer Time: Simmer for at least 30 minutes, or up to 1 hour, stirring occasionally. Simmering allows the flavors to meld together beautifully and the stew to thicken slightly. The longer it simmers, the richer and more flavorful it will become.
3. Check and Adjust Seasoning: After simmering for at least 30 minutes, taste the stew and adjust seasoning as needed. You might need to add more salt, pepper, or a touch more balsamic vinegar or soy sauce to balance the flavors.
4. Remove Bay Leaves and Thyme Sprigs: Before serving, remove the bay leaves and thyme sprigs from the stew.

Step 6: Serve and Garnish

1. Serve Hot: Ladle the warm mushroom stew into bowls.
2. Garnish: Garnish each bowl generously with freshly chopped parsley.
3. Serve with Accompaniments (See “How to Serve” section below for suggestions).