In a deep non-stick skillet or saucepan, add the oil, mushrooms, onion, and garlic and cook them over medium heat until browned.
Add the red wine and cook for 1-2 minutes, until it starts to evaporate.
At this point, add the salt, Italian herbs, onion powder, red pepper flakes, and tomato paste. Stir, and cook for another minute.
Now add the carrots, celery, and vegetable stock. Bring to a boil, reduce the heat to medium-low, cover with a tight lid, and cook for about 30 minutes, until the vegetables are tender.
Make the flour slurry by whisking 1 tablespoon of flour with ⅛ cup of water. Stir in the butter and the slurry into the mushroom sauce. If you’d like, you can add a bit more stock or water to bring the sauce to the desired consistency.
Add the fresh parsley, stir, and your Mushroom Bourguignon is ready.