For the beef: Place the beef into a large nonreactive bowl and add the wine. Wrap tightly with plastic wrap and let marinate overnight in the fridge.
Drain the beef in a colander with a bowl underneath, reserving the marinade. Place the flour, pepper and some salt in a shallow plate and, working in batches, toss the beef in the flour, shaking off any excess.
In a heavy-bottomed pot over medium heat, cook the bacon until the fat has been rendered and the bacon is slightly crispy. Using a slotted spoon, remove the bacon from the pot, leaving the fat in the pot and reserving the cooked bacon.
Working in batches, add the coated beef to the pot with the reserved bacon fat and brown on all sides, about 8 minutes per batch. Transfer the beef from the pot to a bowl and repeat with the remaining beef and seasoned flour until all the beef has been browned. Pour off any excess fat in the pot and increase the heat to high. Pour the sherry into the pot and, using a wooden spoon, scrape up the bits on the bottom of the pot. Pour the liquid over the beef.
For the bouquet garni: Using kitchen string, tie together the celery, parsley stems, thyme, and bay leaves, making a bouquet garni.
For the stew: Melt 3 tablespoons of the butter over medium heat in the same pot used to brown the beef and add the garlic, carrots and onions. Cook until the onions are slightly golden, about 4 minutes. Add the tomato paste and cook, stirring constantly for 1 minute. Add the reserved marinade, beef with juices, cooked bacon and bouquet garni, and bring to a simmer. Cook over medium-low heat, partially covered, until the beef is tender, 2 1/2 to 3 hours.
In a large pot, bring salted water to a boil and blanch the pearl onions for 2 minutes. Drain, rinse under cold water, peel and set aside.
Melt 1 tablespoon butter in a medium saucepan over high heat until the foam subsides. Saute the onions until brown spots appear. Add 1 3/4 cups water, bring to a simmer and partially cover. Season with salt and pepper. Cook until they are tender, about 20 minutes. Uncover and cook until the liquid is reduced and the onions are glazed, about 10 minutes.
Over high heat, melt the remaining tablespoon butter in a large nonstick skillet and saute the mushrooms until they are golden and all the liquid they have released evaporates, 8 to 10 minutes. Season with salt and pepper.
Wait until the last 15 minutes of cooking the stew to add the pearl onions and mushrooms, and then cook for the remaining 15 minutes. Remove the bouquet garni and skim the fat from the stew. Season with salt and pepper.
Serve stew over roasted fingerling potatoes and garnish with chopped parsley.