In a large saucepan, heat on high. Add the oil, onion, garlic and thyme.
Sauté the onion until it starts to turn translucent. Add the beef, salt and pepper, cook until they are browned.
Add the tomato paste and cook for 5 minutes.
Add red wine vinegar and stir well for 5 minutes.
Add the beef stock and bring to a simmer. Simmer uncovered for 1 hour.
Add mushrooms and continue to simmer for another hour.
Remove from heat and stir in sour cream. Add salt and pepper to taste.
Serve immediately over a side of Cauliflower Mash or Keto Egg Noodles.