I love mushroom soup. There are three things to remember in making outstanding mushroom soup.  Good mushrooms, good wine, and good chicken/beef stock.  I've made this mushroom soup for years,  but I include ingredients on hand to vary the basic recipe.  Recipes guide you in a specific direction, and you make your own version by experimenting with what's on hand.  

Mushroom Soup Ingredients

4 large portobellos sliced with stems and gills

4 oz of Maitake mushrooms chopped roughly

4 garlic cloves sliced

2 shallots sliced

1/2 onion sliced

2 tbsp butter

2 tbsp olive oil

1/4 cup of flour

1/2 cup dry sherry

48 oz of chicken stock

32 oz of beef stock

1 tbsp thyme leaves

2 tbsp oregano leaves

3 tbsp of black truffle oil (optional)

Salt and black pepper

In a large soup pot on medium high heat, add butter, oil, shallots, onions and mushrooms.  Season with a little salt and pepper.  Saute for 5 minutes and add the garlic.  Cook for another 2 minutes and add the flour.  Adding the flour makes a roux.   Cook the roux for 1 minute and add the sherry.  Continue cooking to reduce the wine by half.  Add the chicken and beef stock,  bring to a boil and turn down the heat to simmer.  Simmer for 30 minutes and add the herbs.  Puree the soup in batches in a blender until it is silky smooth.  Add a touch of half and half to make it "cream of  mushroom soup" and to lighten the color, if you wish.  However,  it's delicious without the half and half, too.   Finish the soup by seasoning with salt, freshly cracked pepper and truffle oil.  Serve with croutons, creme fraiche, fresh oregano and olive oil.