Blend the cashews with 1 cup of the vegetable stock and set aside.
In a saucepan, heat the oil or vegetable stock. Add the onions and garlic along with a pinch of salt and ground black pepper. Saute, stirring frequently, until the onions turn translucent but do not brown. It is important that you cut the onions really fine so they just melt into the soup.
Add the mushrooms. At this stage you can add a splosh of white wine for more flavor, if you wish. Saute the mushrooms over medium-high heat until they are tender, about 5-8 minutes.
Add the thyme or sage, stir to mix, and then add the all purpose flour or rice flour. Mix well and let the flour cook for a couple of minutes, stirring frequently to let it cook evenly.
Add a cup of the vegetable stock, stirring vigorously as you do so to avoid any lumps from forming. You can also use a whisk to mix at this stage. Add one more cup of stock, continuing to stir, and when it comes to a boil, stir in the blended cashew milk.
Once the soup comes to a boil, you can thin out with more stock to get it to the consistency you like. Check for seasoning and add more salt and pepper as needed. You can also add a tablespoon of soy sauce for more flavor, unless you want to be soy-free.
When the soup comes to a boil, stir, and turn off. Serve hot.