In a large pot over medium-high heat, melt 4 tablespoons of butter. Add the onions, garlic, thyme sprigs, sage, and mushrooms. Cook for 5-8 minutes until onions and mushrooms are soft. Note that the mushrooms will release a lot of water.
Remove several mushrooms and save to garnish bowls. If you want to brown the mushrooms, heat a small sauté pan, add a touch of butter, and cook the mushrooms over medium heat until you achieve the desired color. Set aside for garnish.
Add the wine to the pot and allow it to evaporate for 2 minutes.
Add the chicken stock and bring to a boil. Reduce the heat to a slow simmer for 5 minutes.
Add the heavy cream and blend using an emersion blender until very smooth.
Check the seasoning and add more salt or pepper if needed.
Serve and garnish with reserved mushrooms and thyme.