Place the large pot on the stove. Turn the heat to medium now. Melt the butter until it starts to bubble. Do not let the butter turn brown.

Add the chopped onions to the hot pot. Cook them until they are soft and clear. This should take about five minutes. Stir them often so they do not burn.

Add the sliced mushrooms to the pot now. Cook them until they turn dark brown. They will release a lot of liquid first. Keep cooking until the liquid is all gone.

Stir in the minced garlic and fresh thyme. Cook for only one minute more. You will smell the garlic very quickly. This adds a great layer of flavor.

Sprinkle the flour over the cooked vegetables. Stir well to coat everything evenly. Cook the flour for two minutes. This removes the raw flour taste.

Pour the chicken broth into the pot slowly. Stir constantly to avoid any flour lumps. Bring the liquid to a gentle boil. Then turn the heat down to low.

Let the soup simmer for twenty minutes. This helps the flavors mix together well. The soup will start to thicken slowly. Keep the pot partially covered.

Turn off the heat. Use the blender to make the soup smooth. Be very careful with the hot liquid. You can leave some mushroom chunks if you like.

Stir in the heavy cream very slowly. Add salt and pepper to taste. Heat the soup again for two minutes. Serve it hot in large bowls.