Melt butter in a heavy-bottomed stock pan over medium heat. Add mushrooms and thyme leaves and saute until mushrooms are beginning to soften about 5 minutes.
Add flour to the pan and stir to coat. Allow it to cook for 1 additional minute.
Slowly whisk in marsala wine or stock, whisk until smooth and thick, and then gradually add in the stock and milk, whisking well. Add in the salt, pepper, garlic powder, and onion powder and stir well.
Bring to a boil over medium to medium-high heat and whisk well until the mixture thickened. Anywhere from 2 to 5 minutes.
Use in any recipe that calls for condensed mushroom soup.
Notes
This recipe makes the equivalent of one 10.75-ounce can of condensed cream of mushroom soup and can be used in any recipe that calls for cream of mushroom soup.
Homemade Mushroom soup lasts in the refrigerator for 5 days. I do not recommend freezing.
Use a mixture of button mushrooms, baby portabella mushrooms, cremini mushrooms, or reconstituted dried mushrooms.
Use mushroom, vegetable, chicken, or beef broth
Marsala wine is optional. Feel free to replace it with sherry wine or additional stock in the marsala wine's place. If using wine, be sure to use dry, quality drinking wine.
Dairy Free Cream of Mushroom Soup: In place of butter, use nondairy butter (like Earth Balance), or olive oil. And in place of milk, use additional stock or unsweetened, unflavored non-dairy milk.
Vegetarian Cream of Mushroom Soup: This recipe is vegetarian as long as vegetable or mushroom stock is used for the stock. Do not use chicken or beef stock to keep this vegetarian-friendly.
Vegan Cream of Mushroom Soup: To make a vegan substitute for mushroom soup, use nondairy butter or olive oil in place of the butter, unflavored nondairy milk or stock in place of milk, and use mushroom or vegetable stock (do not use chicken or beef stock.)