1. Preheat the oven to 300 degrees F. Adjust the rack to the bottom third position. 
2. Place a large, heavy-bottomed Dutch oven over medium-high heat. Cook the bacon until browned and crispy. Transfer to a paper towel-lined plate and set aside for now. Don’t drain the pan, but remove any dark bits if necessary.
3. Season the beef cubes with salt and pepper. Working in batches as needed, and with the heat still on med-high, brown the beef in the bacon drippings on all sides until browned and crisped; about 3 to 4 minutes total. NOTE: You can add a little cooking oil to the drippings if things start to look too brown. Transfer the beef to a paper towel-lined tray.
4. Reduce the heat under the pot to medium and add the diced onion, carrots, celery, and bell pepper. Cook until the veggies are tender, stirring occasionally, about 4 to 5 minutes. Season lightly with salt and pepper. Add the tomato paste and garlic and cook for one minute more (stirring). 
5. Sprinkle the flour over top and cook for one minute, stirring. Add the wine and stir to get up any browned bits on the bottom of the pan. Add the stock concentrate, stock,  bay leaves, and thyme. Slide the beef back into the pan. Stir to mix, cover.
6. Place in the oven and let the stew cook for 2.5 hours, until the mixture has thickened/reduced slightly and the beef is fall-apart tender. Pull out the thyme stems and bay leaves. Once removed from the oven, top the stew with the brown butter mushrooms and pearl onions (see below), and the reserved crispy bacon. Alternatively, you can serve the soup and then top each serving with the mushrooms, onions and bacon. 
7. Serve hot with something starchy to sop up the sauce (bread, rice, grits, mashed potatoes, couscous, etc.). 

To make the Brown Butter Mushrooms and Pearl Onions:

1. In a large skillet over medium heat, melt the butter and then allow it to brown. It will stop sputtering and making noise when it’s ready, and it will smell nutty and the milk solids will be visibly golden; takes about 3 to 4 extra minutes after the butter has fully melted. 
2. Add the olive oil to the butter (to prevent burning) and add the mushrooms and thawed pearl onions. Arrange everything in an even layer in the pan, and then allow the veggies to cook and brown undisturbed. Once the mushrooms are nice and golden on the bottoms, flip/stir them, season lightly with salt and pepper, and continue cooking until fully cooked and tender. Serve over the finished stew.