Chop 8 oz of mushrooms into small bite-sized pieces.
Add 1 tbsp of oil and the mushrooms to the pan with the salt, and sauté over medium heat until the mushrooms darken and release their juices.
Add 4 cups of milk, 1 tsp salt, 1/2 tsp garlic powder, 1/4 tsp paprika, and 1/4 tsp black pepper.
Heat until the soup just barely begins to bubble, then reduce the heat to low.
Thicken with the starch method
In a separate bowl, mix 1/4 cup of potato or cornstarch and 1 cup of water. Stir until it dissolves completely.
Pour the starch mixture into the hot soup, stirring constantly.
Continue to heat the soup on low until it thickens and just starts to bubble.
Turn off the heat and serve hot.
Thicken with a roux method
Add 1/4 cup of oil and 1/4 cup of flour to the bottom of a second soup pot. Heat the flour and oil for a minute, then slowly ladle in the hot mushroom broth, whisking between each scoop until all the soup is added and the soup begins to bubble.
Notes
Potato starch gives it a slightly better texture and flavor than corn starch, but if you don't have it, corn starch will work well too.
If you are using thicker soy milk to make this, like Silk brand or equivalent, use 2 cups of milk and 2 cups of water.
You can also use unsweetened plant-based milk in this recipe.
Do not use vanilla-flavored plant milk.
You may also thicken this soup by adding 1/4 cup of oil and 1/4 cup of flour to the bottom of a second soup pot. Heat the flour and oil for a minute, then slowly ladle in the hot broth, whisking between each scoop until all the soup is added and the soup begins to bubble.
If using the oil-and-flour method, still add the extra cup of water; just don't add the cornstarch.