1. Heat oil in a 2-quart saucepan.
2. Add flour and stir with a wooden spoon until the mixture becomes the consistency of wet sand.
3. Add mushrooms and cook 5 minutes more.
4. Pour in stock and soy sauce.
5. Bring to a slow boil and cook 20 to 30 minutes until thickened.
6. Adjust seasoning with apple cider vinegar, sea salt and black pepper.