Bring the water or broth and spices (turmeric, garlic powder, salt, black pepper, nutritional yeast) to a slow boil in a medium-sized soup pot.
Add the chopped celery and simmer at a slow boil for about 8 minutes until celery is tender.
Add the plant-based milk of choice and turn heat to low to just keep warm.
To make the roux
Heat the margarine or oil over medium-low heat and sprinkle in the flour.
Stir with a whisk until it mixes completely and starts to bubble.
Add celery soup one ladle at a time and stir well with the whisk between each ladle full. (Carefully try to scoop out the broth leaving the chunks of celery in the original pot until most of the broth has been added and the thickened broth is smooth and creamy).
Continue to ladle a small amount of the soup into the roux stirring well between each scoop until all of the soup is now in the pot with the roux.
Notes
To make this fat-free you can also use 1/4 cup of cornstarch mixed with 1/2 cup of cold water and add it to the soup at the end of cooking.
The roux method is a little labor-intensive but well worth it for what it does for the richness and taste of the soup.
Do not try this with gluten-free flour mixes that contain sorghum flour. For some reason, it gets a slimy consistency.
To make this lower fat, you can reduce the oil in the roux to 1/4 cup.