Prepare the Ingredients: Begin by washing and slicing the mushrooms. Dice the onion, carrot, and celery, and mince the garlic. Steam the cauliflower florets until tender. Set all ingredients aside.

Sauté the Aromatics: Heat 2 tablespoons of olive oil in a large pot or Dutch oven over medium heat. Add the diced onion and cook until translucent, about 5 minutes. Add the minced garlic and cook for an additional minute, until fragrant.

Cook the Vegetables: Stir in the diced carrot and celery. Sauté for about 5 minutes until the vegetables begin to soften. Add the sliced mushrooms and continue to cook for an additional 8-10 minutes, stirring occasionally, until the mushrooms release their juices and become tender.

Add the Cauliflower and Broth: Add the steamed cauliflower florets to the pot. Pour in the vegetable broth and add the bay leaf. Stir well to combine all ingredients. Bring the mixture to a boil.

Simmer the Soup: Reduce the heat to low and let the soup simmer uncovered for 15-20 minutes. This allows the flavors to meld together and the vegetables to become tender.

Blend the Soup: After simmering, carefully remove the bay leaf. Use an immersion blender to blend the soup directly in the pot until smooth and creamy. Alternatively, transfer the soup in batches to a high-speed blender and blend until smooth.

Add the Milk and Seasonings: Return the blended soup to the pot if using a countertop blender. Stir in the unsweetened almond milk, nutritional yeast, soy sauce, dried thyme, dried rosemary, salt, and pepper.

Thicken the Soup (Optional): If a thicker consistency is desired, melt 2 tablespoons of vegan butter (or additional olive oil) in a separate pan. Stir in 2 tablespoons of flour and cook for 1-2 minutes to create a roux. Gradually whisk this mixture into the soup, allowing it to simmer for an additional 5 minutes to thicken.

Adjust Seasoning: Taste the soup and adjust the seasoning with additional salt and pepper if necessary.

Serve the Soup: Ladle the soup into bowls. Garnish with freshly chopped parsley and sautéed mushroom slices if desired. Serve hot with a side of crusty bread or a fresh green salad.

Store Leftovers: Allow any leftover soup to cool to room temperature before transferring it to airtight containers. Store in the refrigerator for up to 5 days or freeze for up to 3 months. Reheat thoroughly before serving.