Begin by preheating your oven to 350°F.

In a large dutch oven over medium-low heat, cook the bacon pieces until browned and the fat is rendered. Remove the bacon with a slotted spoon and set aside.

Increase the heat to medium-high. Season the beef chunks generously with salt and pepper, and sear them in batches until all sides are browned. Set the seared beef aside.

Reduce the heat to medium and melt 2 tablespoons of butter in the same pot. Add the chopped onions and carrots, sautéing for 2-3 minutes. Stir in the minced garlic and cook for an additional minute.

Incorporate the tomato paste and cook, stirring often, for 2-3 minutes until it darkens. Sprinkle the flour over the vegetables, mixing well, and cook for another 2-3 minutes.

Pour the red wine into the pot, scraping the bottom to release any browned bits. Stir in the beef stock and bouillon, bringing the mixture to a simmer. Return the seared beef and bacon to the pot, along with the thyme sprigs and bay leaves. Cover and transfer the pot to the oven, cooking for 2 1/2 hours.

Around the 2 1/2-hour mark, heat the remaining butter in a skillet over medium-high heat. Once melted and foamy, add the quartered mushrooms and sauté until browned. Then, toss in the defrosted pearl onions and cook for an additional 5 minutes. Season with salt and pepper.

Remove the pot from the oven and stir in the browned mushrooms and onions. Place the pot back in the oven and cook for another 45 to 60 minutes until the beef becomes exceptionally tender.

Once done, remove the pot from the oven and let it rest, covered, for 30 minutes before serving.