In a large dutch oven, melt 4 tablespoon butter over medium-low heat. Add the shallots and sauté until softened but not browned, about 4 minutes. Add 2 of the cloves of minced garlic and the nutmeg and stir to combine. Increase the heat to medium, add the white mushrooms and stir. Cook uncovered, stirring occasionally, until the mushrooms release some liquid, about 7 minutes. Turn heat to medium low, cover and cook until the mushrooms have released all of their liquid, about 20 more minutes.

Add the water, chicken broth and porcini mushrooms. Bring to a simmer and then cover, reduce heat to low, and cook until mushrooms are tender, about 20 minutes.

Meanwhile, melt the remaining 2 tablespoon butter in a separate skillet over medium-low heat. Add the remaining clove of minced garlic, cremini mushrooms and thyme. Season with salt pepper, cover and cook until they release their liquid, about 10 minutes. Uncover and continue to cook until liquid has evaporated and mushrooms are browned, about 3 more minutes. Set aside.

Turn off the heat and use an immersion blender to puree the soup until smooth. Stir in the Madeira, cream, lemon juice & zest and season with salt & pepper to taste. Ladle into bowls, garnish with sautéed mushrooms and serve!