Step 1

Melt butter in a large saucepan or Dutch oven over medium-high heat. Add mushrooms, season with salt and pepper, and cook, stirring frequently, until liquid has evaporated and mushrooms are well-browned, about 12 minutes total. Add onion and cook, stirring, until softened, about 3 minutes. Add garlic and cook until fragrant, about 30 seconds. Add flour and stir to combine.

Step 2

Add sherry or wine and cook until reduced by about half, scraping up browned bits from the bottom of the pan. Add milk, chicken stock, bay leaves, and thyme sprigs and stir to combine. Bring to a bare simmer and cook for 20 minutes.

Step 3

Using tongs, remove bay leaves and thyme. Blend soup with an immersion blender or in batches using a countertop blender. Season to taste with more salt and pepper and a squeeze of lemon juice (if desired). Serve immediately, garnished with minced herbs and olive oil.