Prepare the Beef: Season the beef cubes generously with salt and pepper.
Brown the Beef: In a large skillet, heat the olive oil over medium-high heat. Brown the beef in batches, ensuring each piece gets a good sear. This step adds depth of flavor. Transfer the browned beef to the slow cooker as it’s done.

Cook the Bacon: In the same skillet, add the chopped bacon and cook until crispy. Remove the bacon with a slotted spoon and add it to the slow cooker. Leave the bacon fat in the skillet.
Sauté the Vegetables: Add the chopped onion, sliced carrots, and minced garlic to the skillet with the bacon fat. Cook until the onion is translucent, then stir in the tomato paste.
Deglaze the Skillet: Pour in the red wine, scraping up any browned bits from the bottom of the skillet. This adds flavor to the sauce. Bring the wine to a simmer, then transfer the contents of the skillet to the slow cooker.
Add the Remaining Ingredients: Add the beef broth, Worcestershire sauce, dried thyme, and bay leaves to the slow cooker. Stir to combine all the ingredients.
Slow Cook: Cover the slow cooker and cook on low for 8 hours, or until the beef is incredibly tender and easily shreds.
Add the Mushrooms: About 30 minutes before serving, add the quartered mushrooms to the slow cooker.
Thicken the Sauce: To thicken the sauce, mix the all-purpose flour with a bit of water to form a smooth slurry. Stir the slurry into the slow cooker. Cook for an additional 30 minutes, or until the sauce has thickened.
Serve: Remove the bay leaves before serving. Garnish with freshly chopped parsley. Serve the Beef Bourguignon hot, perhaps over mashed potatoes, egg noodles, or polenta.