In a large skillet over medium heat, add the chopped bacon (or pancetta) and cook until crispy. Remove and set aside, leaving the fat in the pan.
Increase heat to medium-high and brown the beef cubes in batches in the skillet, about 5 minutes per batch. Remove and set aside after browning all pieces.
In the same skillet, add olive oil if needed, then add diced onion and garlic. Sauté until onions are translucent, about 3 minutes.
Add sliced carrots and mushrooms to the skillet, cooking for another 3-4 minutes until they soften slightly.
In the slow cooker, combine the browned beef, crispy bacon, sautéed onions, carrots, garlic, mushrooms, beef broth, tomato paste, thyme, and bay leaf.
Season with salt and pepper to taste, then stir everything to combine.
Cover the slow cooker and cook on low for 7-8 hours or on high for 4-5 hours, until the beef is tender.
Remove the bay leaf before serving. Adjust seasoning if necessary.
Garnish with fresh parsley and serve hot.
Notes
Serve in deep bowls with crusty bread on the side for dipping, and a sprinkle of fresh parsley on top for a pop of color.