Step 1: Prepare the Mushrooms

Clean the mushrooms with a damp paper towel to remove any dirt. Avoid rinsing them under water, as they can absorb moisture and become soggy. Slice them evenly for uniform cooking.

Step 2: Sauté the Aromatics

In a large pot or Dutch oven, heat the butter and olive oil over medium heat. Add the chopped onion and cook for 3-4 minutes, or until softened and translucent. Add the minced garlic and sauté for another 30 seconds, stirring frequently to prevent burning.

Step 3: Cook the Mushrooms

Add the sliced mushrooms to the pot and stir to coat them in the butter and oil mixture. Cook for 8-10 minutes, stirring occasionally, until the mushrooms release their moisture and turn golden brown. Season with salt, pepper, and thyme.

Step 4: Create the Roux

Sprinkle the flour over the mushroom mixture and stir well to combine. Cook for 1-2 minutes to remove the raw flour taste. Slowly pour in the broth while stirring continuously to prevent lumps. Add the bay leaf and bring the mixture to a gentle simmer.

Step 5: Blend the Soup

Using an immersion blender, puree the soup until smooth and creamy. For a chunkier texture, blend only half the soup, leaving some mushroom pieces intact. If using a countertop blender, blend the soup in batches, then return it to the pot.

Step 6: Add the Cream and Milk

Stir in the heavy cream and milk, mixing well. Taste and adjust the seasoning with more salt and pepper if needed. If using white wine or Parmesan cheese, add them at this stage for extra flavor. Simmer for 5 minutes, stirring occasionally.

Step 7: Serve and Garnish

Remove the bay leaf and ladle the soup into bowls. Garnish with chopped parsley or chives, and add croutons or crispy fried onions for added texture. Serve hot with your favorite bread or a simple green salad.