Here is how I make mine.
Mushrooms of your choice cleaned and sliced
finely diced onion or shallot
fresh or dried thyme
low salt chicken stock
Saute mushrooms and onion or shallot, salt and pepper to taste in butter at medium low heat till soft, add the leaves from a sprig of fresh thyme or 1/8 tsp dried thyme cook 2 or three more minutes.
Add several tablespoons of flour, if pan is too dry, add more butter, (the amount of flour and butter will depend on how thick you want the soup.) Cook flour, mushrooms and onions and thyme for a minimum of three minutes mixing well while cooking. Turn up heat to medium and add the chicken stock whisking or stirring quickly to the pot to mix together well and avoid lumps. When smooth turn heat down to low or just to simmer and cook for about 15 minutes, stirring occasionally. If you want to add cream take soup off heat and let stand for a few minutes, then add a few spoons of the soup to a 1/2 cup heavy cream to temper cream, then add cream and soup back into pot and stir to incorporate. Serve and watch the smiles.
I didn't include amounts because I don't measure, I have been making this for a ong time and it all depends on how many people I am feeding but if you cook you know what I mean and you at least have the ingredients..