Mushroom Soup (Vegan)

1 pound fresh portobello or crimini mushrooms, finely diced
1 medium to large onion, diced
2 tablespoons olive oil
¼ cup raw cashews, rinsed
¼ cup arrowroot powder or cornstarch
2 tablespoons onion powder
1 tablespoon salt, or to taste
4 cups water

1. Saute the onion and mushrooms in olive oil until tender. (If you cover the onions and mushroom while cooking over low heat, there is no need to add extra liquids and they cook just fine without the oil).
2. While the mushrooms and onions are cooking, blend cashews, arrowroot powder or cornstarch, onion powder, salt and two cups water until a small amount rubbed between your finger and thumb is smooth and not gritty. This may take as long as five minutes. If you don’t have a very powerful blender, you may want to start out with a little less water until the cashews are blended smooth, adding the rest of the water at the end.
3. Pour blended cashew mixture over the sauteed mushroom mixture, adding the remaining water a little at a time, stirring constantly until thickened. Add more water – or less – until desired thickness is reached.