Prepare your ingredients.Peel, wash, and slice the carrots. Do the same with the celery, slicing it thinly.Peel the shallots and/or pearl onions and halve them lengthwise.Slice or dice the mushrooms, depending on their shape.
Melt the butter in a medium saucepan over medium-high heat and sauté the mushrooms in small batches until golden brown, even slightly charred.Then transfer the mushrooms to a bowl and season with a generous pinch of salt and a few grinds of pepper.
In the same saucepan, sauté the carrots, celery and shallots in oil. Add the chopped garlic after 5 minutes.
Deglaze with the red wine and simmer for 2 minutes.Add the flour and tomato purée and mix well.
Pour in the vegetable stock and add the bouquet garni. Season with salt and pepper.Add the cooked mushrooms, stir, and simmer, covered, over low heat for 30 minutes.
Once the vegetarian beef bourguignon has reduced and the sauce has thickened, remove the bouquet garni.Serve with chopped parsley and your choice of side dish.