Heat the oil in large saucepan over medium heat.
Add onion and cook until soft.
Stir in carrots, mushrooms and celery and cook for about 10 minutes, stir often.
Stir in potato and corn, and cook another 6 minutes.
Add garlic and herbs and cook for 1 minute.
Stir in the rest of the ingredients and bring to a boil. Reduce heat to medium-low and simmer 20 minutes.
Once cooled, blend mixture in blender in batches until smooth or however you like your gravy. When ready to eat, simply reheat and season with salt and pepper.
Recipe adapted from Vegetarian Times.