Start off by chopping the onions, celery, carrots, and mushrooms. This soup is quick to make so have everything ready to go.
Place a large dutch oven or other pot over medium heat. Add olive oil and allow to warm up.
Add in onions and salt. See notes on salt. Cook onions until they are soft and translucent. About 5 minutes.
Add in celery and carrots and stir well to coat in the oil. Sautee, stirring often until they are soft but still have a little bit of a crunch.
Add in mushrooms and stir to coat in oil. Sautee until they start to soften but still have some crunch to them. They will simmer in the stock for a while causing them to become the perfect texture.
Add in the minced garlic and allow to cook for 30 seconds or until fragrant.
Add in the white wine vinegar and stir to incorporate. Allow cooking for about 1 minute.
Add in the dried oregano, thyme, and black pepper.
Add in the beef stock, bring to a low boil, reduce to a simmer and cook for 10 minutes. Taste and add more salt if needed at this time.
Serve warm and enjoy!