Add the sliced mushrooms and diced onion. Cook for 8–10 minutes, stirring occasionally, until the mushrooms release their moisture and the onions are soft. Add the minced garlic and cook for 1 minute, until fragrant.
Sprinkle the flour over the vegetables and stir well to coat. Cook for 1–2 minutes. Slowly pour in the chicken broth while stirring to avoid lumps.
Add the thyme, salt, and pepper. Bring to a gentle simmer and cook for 5–7 minutes, letting the soup thicken.
Use an immersion blender to puree the soup to your desired texture, smooth or slightly chunky.
Reduce the heat to low and stir in the heavy cream. Simmer for another 3–4 minutes (do not boil).
Taste and adjust seasoning if needed. Serve warm, with extra sautéed mushrooms or fresh thyme on top if you’d like.
Cook the Mushrooms Fully: Let the mushrooms cook until they release their moisture and begin to brown. This step builds the deep, savory flavor that makes the soup taste rich and homemade.
Stir the Flour Well: Make sure the flour fully coats the vegetables before adding the broth to prevent lumps in the soup.
Add Broth Slowly: Pouring in the broth gradually while stirring helps keep the soup smooth as it thickens.
Blend Carefully: Use an immersion blender directly in the pot, or blend in batches if using a countertop blender, until you reach your desired texture.
Do Not Boil After Adding Cream: Keep the heat low once the cream is added to avoid curdling and maintain a silky texture.